when u-throw -> uairing with any character I stick jump and use A. I don't stick jump for anything else besides some of my flashier Falco stuff, so I dunno, I'd try stick jumping it, since you can just like, tap forward to dash, roll the stick to upward to full hop and then just hold it there while hitting A to uair.
When it's not a uair, I do exactly what you're talking about, jump with X, aerial with A asap.
When it's not a uair, I do exactly what you're talking about, jump with X, aerial with A asap.