well it is pretty weak
But I have an hypothesis as to why it works well on some people.
Meteor cancelling is the same for every meteor in the game. You have to not press anything for 16 frames, else you're going to eat a penalty and be unable to move for much longer, which is probably going to result in losing a stock.
This is different from other hits, where the weaker the move is, the sooner you can act.
This is very important to know in the case of Ivysaur's belly stomp. It's a weak meteor, as opposed to her dair and, well, most other meteors in the game. So people kinda have the instinct to try to meteor cancel it sooner than they'd try to cancel strong meteors. It's what your intuition tells you to do.
That's where this move becomes dangerous. If you follow your instinct, you're going to eat the penalty and die in the most ridiculous fashion possible. You actually have to wait a bit longer than what seems right, and only then meteor cancel. And a LOT of people fall to this trap.
