I think it's fine that everything that was ranked solely for its niche on Sun should be unranked. I wouldn't consider manual weather teams viable at all; until manual Rain becomes a legitimate archetype, I don't see a niche on manual Sun teams, which have weaker and less varied abusers than manual Rain, being noteworthy for a ranking. The whole point of Sun was that its abusers didn't have to risk themselves to set up; otherwise, I see no reason to use Bellsprout, given its horrible defenses making it difficult to set up, and an inability to further boost its damage leaving it without the OHKO power to actually sweep. C+ seems reasonable for Bulbasaur since its Z-Celebrate set offers a few things over Trick-Or-Treat Pumpkaboo-Small but is generally the worse set, and Pumpkaboo-Small really needs to rise.
I agree that Magnemite should drop because it's not up to par with the other A+ Pokemon - it's much less splashable than Diglett / Foongus and lacks Shellder's uniquely game breaking sweeping potential. I don't know if it should drop all the way to A- right off the bat, though. Magnemite has never been a very reliable answer to various metagame threats; it makes up for this in offensive presence. Many other bird checks are fairly easy to wall - rarely will you find a team that struggles to switch into the weak attacks of Chinchou or Kabuto, so letting them into play isn't particularly punishing. Giving Magnemite a switch-in opportunity is a lot riskier; Scarf Magnemite's Analytic boosted STAB attacks are absurdly threatening to teams that lack one of Ferroseed / Chinchou / Mudbray / Hippopotas, and even then, Magnemite has the means to wear down all of them. SturdyJuice Magnemite also packs more of a punch than Chinchou, and has the added benefit of acting as a general safety net for hyper offense comparable to Sashbra in the sheer number of sweepers it can revenge-kill. Think of Magnemite as a high risk, high reward Chinchou.
Agreeing with Dewpider to drop, there isn't much reason to actually use it on a team outside of it being really cute.
SPL regular season is over and I feel the following have become clear:
Alolan Grimer: A -> A+
This Pokemon is SO GOOD. It feels like a lifetime ago that I didn't look at a Grimer-less team and ask myself, "why do I not have a Grimer-A?" The last time we saw a soft check to the entire metagame of this caliber, Porygon was being nominated for S. Grimer's dedicated niche is relatively small, but it still makes its way onto all sorts of teams because it can back its niche up. A strong Knock Off, limited weaknesses, the bulk to avoid almost every unboosted OHKO, the versatility to fit onto just about any team - if I'm even a tiny bit vulnerable to Abra or Gastly, it's enough of an excuse to include Grimer, and if I'm not, it's probably because I already included it. If you have a dedicated sweeper, it probably benefits from Grimer-A; if you don't have a dedicated sweeper, your team is probably defensive enough to be weak to Abra and Gastly, in which case it benefits from Grimer-A; and if you have multiple sweepers to wear down Abra so that Grimer-A isn't needed in that regard, while somehow not being weak to Gastly, then Grimer-A can act as a nice glue Pokemon overall while still providing Knock Off and Memento, so you might as well run Grimer-A anyways. The only major sweeper that doesn't directly benefit from Grimer-A's trapping is Shellder, but it still appreciates Grimer-A luring in and Mementoing on Ground-types, or perhaps Fire Blasting the Ferroseed, so that it can more easily set up and sweep. Diglett doesn't stop Grimer-A from performing its job at all outside of threatening double switches. It's often just as difficult to leave Grimer-A off a team as it is to use it.
Carvanha: A -> A-
Carvanha is... not great. When Gothita left, it looked like it might still have a fighting (ha) chance with the rise of Tectonic Rage Diglett, but this was not to be - the popularity of Timburr and Croagunk makes it too difficult to justify basing a team around, and its inability to switch in on pretty much anything means it's generally not a great fit on the average team. Carvanha originally rose in viability during mid-late ORAS for its potency when a. paired with a trapper (CarvGoth), and/or b. used as a member of a fishspam or darkspam core.
Its best shot at sweeping is still when it's paired with Tectonic Rage Diglett to KO Croagunk and weakened Timburr, but this is quite difficult to set up, especially now that Croagunk is primarily Nasty Plot and Bulk Up Timburr is becoming the dominant set again. Fishspam simply isn't as big as it used to be - while still a potent strategy, it suffers from the ubiquity of Foongus, Croagunk, Snivy, Cottonee, Ferroseed, and Thunderbolt Staryu, which many teams will have more than one of, as well as tanks that fishspam members will struggle to OHKO, notably Timburr, Alolan Grimer, and Snubbull. Darkspam is still great, but Carvanha tends to be discarded in favour of the new and improved Grimer-A/Vullaby/Scraggy.
While it's certainly still possible to build with Carvanha, it's usually just way easier to build with some other strong offensive threats.
Croagunk: A- -> A
Croagunk has historically suffered from not being able to make much of an impact the first few times it gets into play relative to how easily it is to wear down, leaving it to rely solely on the sheer number of roles it covered to hold its own. However, several recently metagame shifts have been very friendly to it and serve to mitigate its drawbacks. The decrease in Gastly and rise in Alolan Grimer has shifted the metagame so that Nasty Plot Focus Blast has become Croagunk's main set, which gives it all the offensive presence it needs. It still benefits from its godsend of a typing and ability, letting it check Fighting-types, Alolan Grimer, and now frequently Psychic-less Staryu. Croagunk also readily fits onto Fighting spam, arguably the single strongest offensive archetype at the moment, for its sweeping potential and variety of coverage moves. Croagunk is risk-free to the point where it can reasonably compete with Foongus to act as the Poison-type pivot of choice for more offensive teams. Though it's not great as a single dedicated check to most threats due to its vulnerability to lures and simply being worn down, in terms of sheer splashability, Croagunk ranks among the best in the metagame, equal to or above every Pokemon in mid A.
In the current metagame, I feel that Poison-types are nearly as splashable as Fighting-types, to the point where their checks begin to significantly increase in viability. Just as it has always been for Fighting-types, Croagunk not only does what a Poison-type should do for a team, but checks opposing Poison-types as well.
Onix: A- -> A or A+
Of course, I can't mention splashable without mentioning Onix. Reliable Stealth Rock setter, fairly solid Bird check, Volt Switch deterrent, Alolan Grimer check, and Ponyta check, all rolled into one, packing decent offensive presence with its STAB combination and Explosion, denying setup sweepers through Taunt or phazing, all with a touch of unpredictability due to the growing prominence of its Weak Armor sets - Onix just does so much that it tends to get slapped onto a team without a second thought. Because of how much it offers in a single slot, it ranks among the best in everything it does; when you consider any other Stealth Rock setter, bird check, and Ground-type, you first consider what it has to offer over Onix. Despite its weakness to three of the S ranked Pokemon, it is consistently able to perform at least do something throughout the match, whether it's stopping a Vullaby sweep or weakening Staryu into Diglett range, just because it can do so much. Onix is arguably the most dominant utility Pokemon in LC after Staryu; when you think of role compression in LC, Onix should be the first to come to mind.