Is this really true? I only find uair to be useful for punishing a character who's trying to fastfall aerial/fastfall airdodge through you.
Maybe I'm doing uair wrong? But usually if the opponent is trying to airdodge to the side, or is just doing a regular airdodge the uair pushes them to a location where I can't hit them with other aerials (or maybe just upB). I think sometimes I fullhop uair, and I might even be doing midair jump > uair. Would it make sense for those to be less successful? Should I ONLY be doing SH uair?
Also, by "anything" are we only talking aerials? Or is common/possible to stall them with uair close enough to the ground to hit with smash attacks/dtilt?
A midair-jump uair doesn't leave you with a lot to hit them. Unless they are in perfect falling conditions and fastfalling, all you can get out of it is an up b.
First-jump uair though, that's where the money is. When people airdodge, they don't affected by the uair windbox, and will just fall while we can plot our next move. Our uair is fast enough that we'll have time to jump in with nair, bair, fair, another uair, up b and even judgement and dair in some cases.
Sometimes they will recover from the airdodge quickly enough to either be able to dodge our attack or get blown up in the air again by the 2nd uair windbox. In that case, reset the situation with more uairs and condition them to airdodge if they want to get down(or anticipate their landing option and go for a smash).
Of course, nothing is ever as easy as theory makes it sound, but it IS one of my main damagerackers vs characters with slow aerial mobility like MK and Snake.
My flowchart vs MK, Snake, Falco and the likes:
Game starts
I get hit a bunch of times
Get one hit in to launch them in the air
Make it even again
Repeat