Donnie Davis was recruited by Ross and O'Leary to run the system that Shawn Jones ran. He was perfect for that system. It was a similar system that Joe Hamilton ran.
Ross left for the NFL and "he who shall remain nameless" came in and totally screwed up Davis's development...which culminated in the Nameless Coach's decision to bring in Luginbill (who's now a big talking head for ESPN). That decision divided the locker room.
O'Leary came in and slowly built up Davis's confidence. Davis was a big part in O'Leary's and GT's turnaround in the aftermath of the Nameless Coach's tenure. If Davis had played under Friedgen's tutelage, who knows what may have happened to Davis's career. If anything, Davis was just unlucky with the timing and coaching changes. Had Davis been a QB in this zone read/option era he would have been a star.
Donnie Davis eventually led the Arizona Rattlers to an Arena Bowl championship if that means anything.
Davis is far from being the "biggest miss of all".
BTW...Davis is a great example of how much Ma Tech cares about its SAs even far after their playing days. Read this if you haven't already:
http://gtalumnimag.com/2010/02/i-was-robbed-of-a-true-college-experience/