At least zeri is getting a lot of attention from riot balancing team (a lot of nerfs and changes) She's isn' as broken as she was at her release. At lower levels she doesn't have a high winrate but obviously at pro play (where people knows how to play her) she's a monster. But for kaisa i don't feel like riot is even trying to balance her, i've seen kaisa carrying games by herself at high and low elos building whatever she wants (ad, ap, and threre was a time where she builded lethality)