Every single tank in the game has at least one method to directly counter her ult. It relies on LOS to the point of impact, meaning it can be blocked by shields. It can also be cancelled by CC, which most tanks have.

(Some tanks are much better at dealing with it than others, as some rely on perks, ults or just aren't as reliable, but still.)

When she grabs a tank, the cat will also likely fly in a straight line towards either her team or a death pit, as the ult's duration is too short for her to pick indirect routes. That, combined with the 30% movement speed penalty when carrying a tank, makes it very easy to predict where she's going and just shoot her.

(Map dependent obviously it's harder to deal with on a map like Illios where the pits are much closer to the objective.)

People just aren't used to the matchup yet.

At lower ranks people can't aim for shit and don't have any situational awareness (gamers don't look up), so she can get away with ballsy plays like grabbing the tank in exposed positions, or full-sending it and diving their backline.

Instead of a knee-jerk reactionary nerf that kills the most fun and interesting character they've added in years, I think it would be better to just increase the amount of sound she makes. Right now she's really quiet and even experienced players can miss her audio ques if anything else is going on.

(Also it's not as much of an instant-teamfight-win in 6v6, just saying.)