There's a reason why Varus can't have a strong poke, DPS and hybrid damage in a single build path, because it'd be fucking overpowered. Imagine lethality Varus breaking AS cap and destroying your tanks with %HP damage while reaching 30% CDR. This is pretty much what Kaisa does.
Gut her already, this champion has been in every single pro game since her release because she has no weaknesses, it isn't only about being able to build zhonyas.
Kaisa should have to choose between being an assassin or high DPS lategame hypercarry not both, get to work Riot, it has been enough of putting up with this garbage design.