Eh?
Dthrow->Uair true combos against a lot of characters. Depending on their weight/size and such, the %s are different, but its generally between 85%-125%. In fact, I haven't found a character yet that you can't true combo.
Characters I've gotten it to true combo so far: Cpt Falcon, Mewtwo, Fox, Lucari, Olimar, Mario, Luigi, ZSS.... Plus another 1 or 2 that I'm forgetting..
Note: I have left trigger set to jump, so I can easily buffer a full jump up air after throwing.
EDIT: Ok, I'm having difficulty landing it on the big fat characters.. Couldn't get it to true combo on DK and Bowser.. I got it to true combo on Jigglypuff and Kirby though, and a couple mid weight characters like Pit and Marth.. So yeah, it seems like you can true combo dthrow-uair on most of the cast, except possibly for the heavy weight characters.