All things being equal, a CFL starter ought to win a Grey Cup every eight or nine years, so Allen won them at a pretty good clip. I'm trying to think of guys who did better in Grey Cups than Allen:
Moon, obviously, went 5-0 in Grey Cups over six seasons, though he didn't start in two of those wins.
Flutie was 3-1 in eight seasons.
Ray has gone 3-0 in twelve seasons, not counting 2014.
Calvillo was 3-5 in twenty seasons.
McManus was 3-2 in seventeen seasons, but had only garbage time in the 1990 win and came off the bench for the 1994 win. He played a hell of a game in the '96 loss though.
I think I agree with the people who are saying that Damon Allen that he was a B+ QB with an A+ career. But if I had to choose a starter for a Grey Cup game, it'd be a tough call between him, Ray, Flutie, or Moon. And Moon and Flutie had stacked teams for their wins. Allen won the Grey Cup with good teams, but never dominating ones.