Sounds like you're describing Azir syndrome, which may be a reasonable description of her current balance state, but that still doesn't make promoting a never-detach playstyle the right way to nerf her. Her passive is important to giving her healthy gameplay.
The bigger issue for her balance vs. elo curve IMO is that in pro she rarely/never gets screwed over by her ride going in an unexpected direction, depriving her Q of range, or jumping into 4 people believing a cat is as good as a Kayle ult. All of which are regular occurrences in soloq. Likewise allies moving out of her W range when she needs a way out (Lee Sin/Braum/Rakan can have that problem too, but they can survive it much more often).
But those things are intrinsic to her champion concept, I think the only way they can be fixed is for regular players to actually learn what to do (and not to do) when you have a kitty. Which could take a long time.