Are there fighting types that would KO Pachi but not Corsola about? No.
...Kabuto? Riolu? Both of those are BRUTAL to Pachirisu, and nowhere near as much to Corsola.
...Then again, no one plays either, so Pachi's still better (assume infinate resources available for deck building). Hm.
I guess what would be more useful is to consider the decks that play Pachirisu and see which ones could use Corsola with no drawbacks (still able to find three pokemon with ease that are useful). I know Skittles comes to mind as one of these. Old-school Magmortar/Typholosion/Delcatty comes to mind too, but with cards like Glaceon and Empoleon, such decks are rather... scary. Plox could replace the Pachis they might play with Corsolas, and still be fine. Less then ideal (ew, Fire type Ralts), but fine. Hurricane gets away with it...
Hm. The only deck that actually plays Pachi that I could think of being worse with Corsola is... Magmortar/Blaziken. Obviously Corsola is unable to do even its searching ability efficiently in that deck. Empoleon based decks might dislike it too, but few actually use Pachirisu. ...Is that really it, for decks that care about the difference between the two? Seems kinda low... :/
((Yes, I do realize that the ability to take a Pachirisu and look for 2 Cyndaquils and a Magmar is much more useful then the restrictions of Pachirisu. But does Corsola have more problems setting up the core of that deck? Not really. Hm.))