EDIT:
I misread, so this is a Kat complaint thread. I thought it was about Poppy.
Kat can be easily countered by simply using a hard CC at her when she ults, which basically just destroys her. This includes, but not limited to, using Poppy's E OR R on her when she channels ulti. So you wouldn't have to worry about Kat's dash, since she wouldn't be doing anything if you're Poppy anyway.
Not to mention given that Kat has a pretty rocky early to mid game due to her high set up time (that is also telegraphed) and the fact she is basically a non-champion before getting her Hextech Gunblade, as long as you keep her in check she becomes instantly irrelevant for the game.