Viktor a bit strong?

Okay now maybe i'm just not that familar with balance. But i feel like viktor has a overloaded kit being able to do many things and have pratically no downside. Massive aoe damage? Check, His ult has that. Massive single target point and click damage? Check his q has that all by itself. Hes ranged he has a aoe stun that if you are melee and try to kill him you most likely are going to get stunned He ends up building rylias so he has a permaslow he has pretty low cooldowns he has a decent early game a good mid game and an AMAZING lategame. Hes good in teamfights its hard to catch him out unless he is being very stupid with q shield and w and his massive damage x.x. So maybe i'm just stupid but is it just me or does he have few downsides? Honestly none come to mind but i never really played the champ