There are ringless great QBs. Why is that?
Compared to Brady... Jim Kelly was a stiff. He was a train wreck in the playoffs generally and flat out horrendous in the Super Bowls. The only Super Bowl he didn't completely gag was the first one against the Giants. Even still the best thing he did that game was handoff to Thurman Thomas. They should have won that first one because they got smoked in the next three. Kelly was a disaster against Washington, throwing 4 picks before he threw 2 garbage time TD's. The back-to-back losses to the Cowboys, they should forfeited and saved themselves the embarrassment.
Kelly, 4 Super Bowls (0-4), 2 TD's, 7 INT's
John Elway, he sucked in his Super Bowl appearances as well. The 0-3 with Reeves... Elway was awful in each and the games weren't competitive at all. The two he won with Shanahan, the first was won on the legs of Terrell Davis, the second, Elway was fine, he hit Rod Smith with an 80-yard bomb, but their defense carried the day (forcing a bunch of turnovers). Bottom line, Elway never wins a Super Bowl if not for Terrell Davis.
Elway, 5 Super Bowls (2-3), 3 TD's, 8 INT's
Dan Marino, ugh... as great as I think he was, the fact is he made way too many mistakes in the playoffs. 24 picks in 18 games. As he was fading toward the latter part of his career, hindered by injuries, he only got much worse in the playoffs. Among the bigger underachievements in NFL history was Marino not winning a Super Bowl. The one he got to, he got completed outperformed by Montana.
My takeaway... Brady has been consistently good and phenomenally clutch in the postseason. Unlike these other three all-time greats who combined for 10 Super Bowl appearances, 2 wins, 8 losses, 6 TD's and 17 INT's.
Brady... 9 Super Bowls, 6 wins, 3 losses, 18 TD's and 6 INT's.
So yeah, while coaches matter, sometimes they matter less, and sometimes they don't matter at all. In those combined 8 Super Bowl losses for Kelly, Elway and Marino, they had 5 TD's and 16 INT's... no coach is overcoming that mess. It's a lot easier for a coach to win Super Bowls when he has the greatest quarterback of all-time putting the team in the lead in 9 out of 9 times late in the 4th quarter.