Despite how OP transformed Kayn is (not original Kayn)
He certainly does feel like dog-shit to play right now, this is coming from somebody who pretty much mains Kayn atm.
Takes 12-16 minutes to transform, on bad games 20 minutes. Game surrenders at 20 minutes or 30 minutes - practically never at 35+ minutes does a game even exist.
If you're going to completely Overwatch / HOTS your "LoL" game then maybe make it so that champions who do scale well later on, can actually get to that point with reasonable time to enjoy themselves. At the moment, Kayn is defeated by:

Throughout the current early, mid, late game (10 mins is early game, 15 minutes is now the mid-game and 20-25 minutes is pretty much the late game.) Kayn is outright bested by these guys and have already won the game because of Kayns lack of strength early on.