I don't recall Tony needing his legs to fly around much in the suit, much less that that portion couldn't be controlled otherwise.
That said, Rhodey's crippling in Cap 3 always bugged me. Cheadle doesn't have enough screen time in these movies for any impact to matter, and its not like Marvel needs to set up a parapalegic hero ahead of time. The only way it makes any sense to me is:
At the end of Avengers 4, Tony gets the full on Infinity Gauntlet. Tony's God Complex issues that have been building for a decade finally come to a head, and he brings Cap and whomever else get killed in 3 back to life (all the Chris Evans contract smoke convinces me there's fire there), restores Rhodey's spine, etc., and goes on about how he can finally "Fix Everything". Then Cap gives him the old "You know what you have to do" speech, and Tony negates the gauntlet out of existence (which is the only way to write the gauntlet out of that universe), negating everything Thanos / Tony did with the full gauntlet (and rekilling Cap, recrippling Rhodey, etc.)
Think about it: The big twist ending of 3 is they kill off Cap. Then the comic book nerds tell everyone in the gap that the gauntlet will bring Cap back to life in the next movie. Then the final trailer has a bit of Cap alive again. Then the twist ending of 4 is that Cap stays dead. Then all those announced but untitled 2020 Marvel releases get revealed: The Invincible Iron Man (with Rhodey flying), Captain Bucky, etc.