Doug was a great college QB
Brady was just very good; not spectacular. He always relied on fundamentals. Rehbein was the only one to see his clutch ability.
Flutie (like Montana) made big plays at crucial times, but was more athletically impressive. Most of the USFL guys eventually got a chance in the NFL and were terrific. Flutie was shat upon because of his height.
But when he got the chance there and in the CFL, he demonstrated all the leadership, durability, determination and championship clutchness of Brady.
Everybody gets old. Doug only went to Buffalo after considering retirement. By 2001 it was impressive and unusual for a guy his age to even be playing. Tom's doing what he does now because he never relied on physical ability as his primary asset.
The season and career rushing and passing records Flutie set in the CFL will probably never be broken, and his six MVP'S and three titles speak for themselves.
Simply put, had he been given the kind of treatment and teams that Young, Kelly, Aikman and Elway had been, I expect he would have done better than all of them. In terms of winning, because that was always his priority. Like Brady & Russell.
The other guys mentioned above had coaches and owners who believed in them, and didn't yank them when they played crappily - which they all did, and which people like to pretend Doug did when he was here, despite obviously leading the Patriots to the brink of the playoffs even with a head coach who hated him. By contrast, Young spent all his time in Tampa running for his life.