Fair enough, but you are making Chikorita look significantly worse than it actually is.
I'll answer you, but one disclaimer first, I was talking about GSC in my post. The games that introduced Chikorita as a starter. Things might be better or worse for Chikorita in HGSS but I don't know. I'm not nearly as familiar with the remakes.
How? Yes, those types resist Grass, but what are those Gyms going against Chikorita/Beyleaf? In GSC, Chikorita learns Reflect at lv12 and only Pidgeotto has a super effective move against the starter while in HGSS, it might not get that move early on, Pidgeotto's Gust will hit for less damage because of the poor special attack stat
Gust is physical in GSC. Pidgeotto outspeeds. Falkner's gimmick is lowering accuracy. Pidgeotto will be outspeeding and targetting Chikorita with super effective STAB Gust while you're praying that your Tackle doesn't miss.
Even if you didn't get Mud-Slap'd, Tackle can still miss (95% accuracy of trolling). Cyndaquil and Totodile at least are trying to land neutral STAB moves with base 100% accuracy. Chikorita has the weakest attack stat + the weakest and most unreliable move in this scenario.
It's also not true that Pidgeotto is the only Pokémon with a Flying-type move. One of the trainers on the way to Falkner has a Peck Spearow. Will it beat your Chikorita if you don't play like an idiot? Probably not. Will it inflict more damage than you would have liked and force you to backtrack to the Pokémon Center to heal your Chikorita? Maybe, but definitely more likely for a Chikorita run than a Cyndaquil or Totodile run. This might not be a big deal to most people, it wouldn't be to me, I don't care about speed running, BUT it is also not efficient since you either waste extra time or extra money/items/resources on healing because the other two starters would have comparably taken less damage.
Against Bugsy, you have only to fear Scypher who has a 10 base power STAB move in gen 2 and while it has U-Turn in HGSS, you can set up Reflect and heal up with Synthesis after taking one U-Turn. What are Metapod and Kokuna going to do to it? Kokuna might win the Poison Stall war with Harden in GSC but you can still win with double resisted Razor Leaf.
The first Fury Cutter is the weak one. The second Fury Cutter will damage you heavily. By the third Fury Cutter, your poor Chikorita will be dead. Reflect or not. Scyther has the stats of a fully-evolved Pokémon while you're trying to land Poison Powder and Tackle for mediocre damage at best.
Metapod and Kakuna are completely pointless, but even here Chikorita is comparably the worst choice. Cyndaquil just fries them in two turns. Next.
Totodile at least has Water Gun to not get stalled by fucking Harden.
Chikorita needs to break a defense that increases with every turn, wasting a bunch of time. Will Chikorita lose to Metapod or Kakuna? Of course not. Will it waste a bunch of time and take ten times as long as Cyndaquil? You can answer that question yourself.
The rest of the Gym before Bugsy isn't much better.
Cyndaquil runs through it without taking hostages.
Totodile at least has a neutral STAB to hit everything that isn't Paras for damage.
Chikorita is still stuck relying on Tackle two Gyms in.
In GSC, you have Reflect and Poison Powder before Whitney. Yes, Miltank is faster but of all starters, Chikorita has the best match up and can outlast the cow unless you are unable to attack at all.
In HGSS, Miltank might be physically bulkier to Razor Leaf but the addition of an early Synthetis allows you to still beat it one on one unless your opponent haxes you to death.
There is really nothing threatening in Goldenrod Gym besides Whitney.
There is also no way to reliably predict the outcome of that battle, no matter which starter you choose to use. The whole Whitney battle is one big fucked up RNG extravaganza.
Between
- Metronome Clefairy
- Attract Miltank
- Stomp flinches
- Smokescreen Quilava
- 75% Accuracy Poison Powder
- Headbutt flinches (Quilava can outspeed Miltank and fish)
- potential Ember burns (only 10% but battles against Miltank tend to be very long)
- Rollout damage rolls which can vary severely
- ...
you will have fun.
I'm not trying to say that Chikorita is the only one that has a hard time against Whitney, because they all three suffer hard here.
None of them are able to end the battle fast and clean. All three starters need items to actually stay alive and win 1on1.
BUT Quilava, while being weak to Rollout, is the only one that can turn the odds for the long game in its favor thx to Smokescreen*. It is also the fastest of the three starters and is the only one that has a chance to outspeed Miltank and fish for potential flinches with Headbutt. It can even fish for burns with Charcoal Ember once Miltank's accuracy is crippled.
Reflect runs out. Poison Powder damage doesn't grow over time, so can be healed by Milk Drink. There is no way for Miltank to heal a reduced accuracy and the lower accuracy won't end after 5 turns.
Croconaw is probably the weakest choice here, since Bayleef makes up for the lower physical bulk with Reflect (yes Croconaw has higher physical bulk than Bayleef) and actually has Miracle Seed Razor Leaf compared to Water Gun, Ice Punch and Headbutt.
None of the starters has the real obvious advantage here. Whitney is hard for every starter. The difference is in the bigger picture.
While they all have a hard time against Whitney and will lose if the RNG decides to make you lose, Cyndaquil and Totodile actually provide outstanding value in other parts of the game. Chikorita is not great against Whitney... or much else these games have to offer.
*I know that all three starters learn Mud-Slap by TM at that point in the game to get the same utility as Smokescreen Quilava, but I did not consider it for one simple reason. It is a unique TM.
Headbutt can be bought indefinitely. Mud-Slap is gone for good once you use it.
You have a better match up against Magnemite with Chikorita than with Charmander against Brock. Magnemite can cripple you with T-Wave but still takes decent damage from your Razor Leaf on in HGSS's case, Magical Leaf. You can also use the Magnemites to set up Reflect to win against Steelix.
What does Charmander have to do with anything? Or Brock for that matter?
Bayleef/Meganium can't poison the Magnemite. It is stuck using Razor Leaf, Headbutt/Body Slam or Rock Smash while wasting time against Thunder Wave + Supersonic parafusion.
Once it gets past that, it most likely is paralyzed and maybe confused.
Steelix comes in and outspeeds now. If you're a Bayleef user, pray that you don't get Screech into Iron Tail hit or it's over.
Quilava can avoid the whole parafusion bullshit because it just kills the Magnemite with STAB Charcoal Flame Wheel. It is also not too afraid of non-STAB Rock Throw or uneffective Iron Tail.
Feraligatr has most likely fully evolved by now and is spamming unresisted Mystic Water STAB 95 base power Surf against unevolved Magnemite and Steelix.
Against the ice types, you have the best chances to win with Chikorita ironicly because the other starters can't hit anything but Piloswine for super effective damage. Besides, Meganium will likely be faster than any of those Pokemon at that point.
That's just wrong.
All the starters should have fully-evolved by now with the whole Team Rocket arc bs.
Typhlosion runs into the Gym with an Ice-type resistance, STAB Charcoal Flame Wheel + Thunder Punch coverage and the highest Special Attack and Speed stats of all three starters.
Feraligatr runs into the Gym with an Ice-type resistance, STAB Surf for the Ground-types + Slash for the Jynx, Seel, Dewgong, Shellder and Cloyster coming from the highest Attack stat of all three starters.
Meganium runs into the Gym with an Ice-type weakness, STAB Miracle Seed Razor Leaf (low base power of 55 and troll accuracy of 95%) + Body Slam coverage coming from the weakest offensive stats of all three starters.
If it does not get crits left and right, Meganium is in a world of pain now. It is the only one that surely gets targetted by Ice-type moves like Jynx' Ice Punch and all the Powder Snow and therefore runs the highest risk of getting frozen.
It is the only one of the three that can miss a move and also the only one of the three that needs every move to land. Flame Wheel, Thunder Punch, Surf and Slash won't miss. Razor Leaf won't miss... until it does.
You most likely won't need to heal Typhlosion or Feraligatr while tackling this Gym. You will most likely need to heal Meganium while doing the same. Again, wasted time, wasted resources, efficiency.
Here you have the best advantage with Meganium in GCS because of Maganium's raw bulk. Gator will need Ice Punch to hit anything Super Effectively and fears Thunderbolt from the Second Dragonair. In HGSS, Gator has the best match up because of level up ice fang and the lack of Super Effective moves against it. Meganium fears Fire Blast but otherwise it can outstall the rest of the Dragons.
Feraligatr resists the Seadra + Kingdra while hitting the rest with a super effective move. It is literally the only good starter for this Gym. (Ice Punch can be bought and doesn't cost much. Blizzard can be bought but costs more.)
Typhlosion is just wrong for the job and easily the worst.
Meganium will do better than Typhlosion, no contest. It will probably win in the end, but by the time it does, Feraligatr is already half way to the league.
If you want to say that Meganium isn't the worst here, I wholeheartedly agree.
If you want to say that the value Meganium provides in this Gym makes up for all the other bullshit that a Meganium user had to deal with on his way to Clair, I wholeheartedly disagree.
There is nothing efficient or great about the value that Meganium provides in Blackthorn Gym besides maybe killing a few Horsea and Seadra and even Typhlosion can do that with Thunder Punch.
Non of Will's Pokemon except of Jynx will hit you for Super Effective Damage in GSC, while in HGSS, you can set tank their moves and set up an Reflect on their face. In HGSS, you can also hit Slowbro for good damage with Razor Leaf regardless of Amnesia boost
Yeah, but you won't hit them for super effective damage either. While they're spamming neutral STAB Psychic, you're trying to not waste too many Body Slam PP because you actually need them for the rest of the league. Razor Leaf won't take you far at all in this place.
Typhlosion and Feraligatr more or less run through Will.
Meganium always needs a turn more, another Ether, another Potion, more PP, more time while still being stuck with 55 base power 95% accuracy Razor Leaf at the league, which is just sad.
Exeggutor can also Reflect to waste even more of your Body Slam PP.
You also forgot to mention that while Meganium only gets hit for super effective damage by Jynx' Ice Punch, Typhlosion and Feraligatr don't get hit for super effective damage at all against Will (in GSC). Slowbro has no Water-type move. Exeggutor has no Grass-type attack.
Umbreon will cause trouble to any of the three starters. Meganium can still cripple it with Bodyslam or Poison Powder. Besides in HGSS, non of the other Pokemon besides Houndoom will cause trouble against Meganium offensively. The rest will be haxed by Bodyslam bar Gengar (unless you are using Earthquake).
In HGSS, you have to look out for Mukurow in addition because of Drillpeck, but with Reflect it would need to rely on a crit to do significant damage.
Meganium simply needs more attacks to get past Umbreon than Typhlosion and Feraligatr, which means more chances to hit yourself in confusion... more turns when you take a Sand-Attack to the face...
You're right that all the starters can get stalled for a few turns by Umbreon, but Meganium is also stuck with the weakest move and the lowest offensive stats while trying to land an attack through confusion and Sand-Attack.
Vileplume walls you, can paralyze you with Stun Spore, stay alive and waste even more time with Moonlight and has Acid to actually hit you for damage (in GSC).
Murkrow at least forces you to waste another Body Slam, because your STAB is still useless.
Gengar just stands there licking you while Curse slowly kills you.
Houndoom used Flamethrower it is super effective!
Earthquake is like the most valuable TM in the game. Wasting it on Meganium... yeah...
Against Lance, you sadly need to rely on your other team mates. Depeding on what you are running on your Meganium, you can somewhat deal with Lance. Obviously if you have STAB, Poison Powder, Bodyslam, Reflect, you cant stall out the Dragonites. Meganium still has the option of Lightscreen per level up. However, non of Lance's Pokemon are immun to Paralysis from Bodyslam or Poison Powder.
Typhlosion at least can Thunder Punch Gyarados and take on Charizard.
Feraligatr roflstomps Lance.
Meganium has reached the climax of the journey and is still stuck using Poison Powder and STAB Razor Leaf. There is also no chance in hell, that you still have Body Slam PP left after the last four battles unless you stockpiled Ether and Elixir like crazy and even if you did...
Meganium once again needs more time and more resources for less value.
EDIT: I agree with the following post and I have said anything that I had to say anyway.