There are lots of outliers of short kings being solid QBs, especially in the college game. Ty Detmer, Eric Crouch, and Johnny Manziel also both won the Heisman and both were under 6 feet. Manziel, like Wilson, is from a more modern version of the game with huge lineman as well so it can be done with a short guy--especially if he has a wiggle.
Generally, those guys all have a couple of qualities that are + or ++, whether it's a big arm, the ability to run the ball, the ability to make broken plays, footwork/mechanics, or outstanding accuracy.
I don't think Colandrea has any of those really, maybe a + athleticism, but I don't know that he has anything that I'd judge to be ++. He doesn't have great mechanics though, and that's where I am hoping Mullen can lift him up. Orji probably has more + characteristics, but again, nothing that I'd call ++.
If Mullen can fix footwork and throwing mechanics either of these guys will take a huge step forward. But Orgi had 3 years with Harbaugh who is pretty solid as a QB coach, he helped develop Luck and did an excellent job with Smith and Kaepernick in the pros. Colandrea came from Tony Elliot's program who was the QB guru on Clemson's staff where he coached and developed both Watson and Lawrence. And that's probably why I have my doubts. It wasn't like these guys were struggling under Ed Orgeron and not getting any good QB development.