If you made Rengar clunky with half second cooldowns after abilities he might be "healthy".
But then Rengar players would feel as screwed as Akali players.
But then Rengar players would feel as screwed as Akali players.
How to fix it :
Remove Rengar
Only if you add this to other champions like Riven/Kha'zix (not sure if he can still do Q in jump though)/others able to cancel their animation.