Really, statistically he wasn't that overpowering. You look through his career and he had very few seasons that jump off the page at you. He only had one season with 30+ TD passes. Even in that season he barely broke 3,000 yards.
9th all time in completions
11th in attempts.
10th in yards
9th in TD's.
8th in rating
11th in completion percentage.
By stats alone he's a Borderline Top 10 guy. At the end of the day though the guy was a flat out winner and in the playoffs he was fantastic. That bumps him back up the list in a lot of ways and makes him a borderline Top 5 guy. I don't have an argument against all the rings and I won't even try. But I guess I'm just not as blown away with Montana as many are.
Untias
Manning
Marino
Elway/Montana/Favre/Tarkenton
IMO is where it begins.
After that it becomes tough. Because you go back any further than Tark(outside of Unitas) and era REALLY become an issue. How do you evaluate guys like Baugh, Luckman, Layne, Starr, Dawson, Graham, Van Brocklin, Tittle, etc against the NFL post 1970...especially against the next tier of modern QBs like Aikman, Kelly, Staubach, Bradshaw, Fouts, Moon etc.