Ya need the claw grip to effectively use a PS2/3 controller.
This also means you need hands that normal human beings don't have.
What a useless controller.
ANYWAY! I find that doing these platform drop Uairs requires good sensitivity with the joystick. If you smash it, you will jump, so you need to move it up quickly to the neutral position and then just squeak it a bit more as if doing a Utilt on the ground. It doesn't need to be all the way up, just barely over the neutral point, and it'll register. Hard as hell to do, but if you hold the controller like DMoogle (or Blue Yoshi, can't remember), then it'll be easier since you'll have better control.