Hold up a sec you guys, I JUST realized the one practical application to Misty Surge's primary effect!
Remember, unlike the other primary effects (giving a weather-style boost to its type), this one just grants all Pokémon under its effect a resistance to Dragon. It does not weaken the user's move! It simply grants the target a resistance.
This means that if you use a grounded Dragon on your team like Garchomp, Garchomp is no longer weak to Dragon.
However, if your opponent uses a flying Dragon like Dragonite, Salamence, Hydreigon, or the almighty (regular) Altaria, they aren't granted a resistance. You can now leave Garchomp in against them as it's no longer weak to their Draco Meteors or their Outrages, but they're still weak to Garchomp's.
And if you think "Yeah, but Garchomp is still being neutered if its opponent IS grounded", bear in mind that Garchomp is likely relying on Earthquake for a majority of the match, and only pulls out DM/Outrage against flying targets in the first place. Even if the opponent is Mega Charizard X, you still win out as 'zard needs to use Dragon Claw, but you can still use Earthquake.
This really won't be a game changer, but if you happen to be running a grounded dragon like Garchomp alongside Fini, just remember that you still have free reign against flying opponents, and you needn't run if your opponent has a Dragon type move! (If only Dragon coverage was actually a thing anyone used.)