What it comes down to is football being a team sport. John Elway is a perfect example. He was absolutely horrible in his super bowl appearances before the Broncos got Terrell Davis and established a dominant running game. With Davis, Elway won two titles there.
Joe Montana was a perfect fit for Bill Walsh's offense that featured a short passing game and required an accurate passer. Montana was super. But, I'd guess Trent Dilfer or Jeff Hostettler win a couple of titles (maybe not three) with that talent around them. That's not to demean Montana, but SF was one of the best super bowl teams ever.
While Dan Marino's style was different from Montana's, I believe his success would have been similar. I always ranked Montana as the best quarterback of his era with Marino second. But I will say this for Marino he lifted the talent level on the Dolphins perhaps more than any quarterback could have.
Another poster mentioned that Miami's talent sometimes looked like maybe three wins, but they would hang in the playoff race. Not sure that Montana could have done that with the Dolphins. Of course we'll never know, but that's the kind of discussion that makes the football offseason less boring.
It's one of those things that is obviously debatable...can never be proven...but is open to opinion and fun to talk about.
I have always stated that If Montana and Marino had gone to the opposite teams....Marino would still be in the hall of fame except with at least 5 rings...and Montana would not be in the hall.
I don't say this to demean Montana...but just as Bob Griese suffers some from critics who devalue him due to the high quality of the teams he enjoyed in the early 70's....Montana also enjoyed an extremely high level of talent and overall team strength that made a very good quarterback reach the conversations of greatest ever...even though I personally don't put him in that conversation.
I don't think Montana gets the 1984 Dolphins to Super Bowl 19 to play the Niners...who were an amazing team that nearly went undefeated with only one loss. Marino lifted a Dolphin team with the 19th ranked defense(out of 28)...and a pedistrian running game to that game.
To me...Montana was a somewhat higher level Bob Griese.
1983
If Marino had been drafted in 1983 by SanFrancisco and Montana by Miami in 1979...Marino may have challenged for a title in his rookie year, it would have been interesting. The Niners lost a lot close games that year finishing 10-6....and barely lost the NFC title game to Washington. Marino, even in his pro bowl rookie season...might have made a difference.
1984
No doubt in my mind Marino takes the 1984 Niners all the way...maybe undefeated. The Niners only loss was a 3 point loss to the Steelers...the same Steelers Marino waxed in the AFC Championship game 48-21 with his Dolphins
1985
This was the first of four consecutive seasons where Montana was either hurt(1986)...or had awful playoff performances which eliminated them. Montana had a 65.6 QB rating in their playoff loss with no touchdowns. Marino meanwhile was in his prime and led a less than amazing Dolphin team to 12-4 and to the brink of Super Bowl 20. Had Miami not turned the ball over 7 times(5 fumbles) they would have won this swan song for the Orange Bowl, and we get Ali-Frazier 2. Marino was in their heads, and was hungry from the previous years failure in Super Bowl 19...would have been great to see this rematch, odds are we lose this one...but Marino would have had a punchers chance(so to speak).
I think Marino has a chance with the Niners...and if he overcame the Bears in the NFC championship game another ring would have been his.
1986
Montana had a bad year, only played in 8 regular season games, getting hurt...threw more interceptions than touchdowns...yet, the Niners still went 10-5-1 and won their division with Jeff Kemp and Mike Morowski filling in. With Dan Marino throwing to Jerry Rice? The same Dan Marino who threw 44 touchdowns that year...he could have made the difference. If they get past the Giants in the wildcard game...I think they win it all.
1987
There was not much for Marino to improve on for Niners in the regular season as the Niners went 14-2 and Montana played very well, Jerry Rice in his prime. But in huge playoff upset to the 8 win Vikings...Montana was awful(funny how people forget this awful stretch of years of Montana in the playoffs)...I have to believe Marino leads this team all the way for at least his 2nd ring(potentially more).
1988
Niners win the Super Bowl...I have to believe Dan Marino in his prime leads them there as well for his 3rd ring.
1989
Niners win again...again, no doubt Dan Marino in his prime leads this 14-2 team there as well for his 4th ring.
1990
Niners fail to 3 peat losing by 2 points...I say Marino in his prime with Jerry Rice lifts them over the Giants in the NFC championship game and win it all....Marino gets his 5th ring.
1991
Montana is hurt...Young takes over and they go 10-6...fail to make the playoffs. It's debatable, but I give Marino and Rice a decent chance to beat Washington(the eventual champion) in the NFC playoffs and possibly 4 peat. But for the purposes of this subject...I'm not counting this one as a win...only a possibility.
1992
Steve Young takes over...Niners go 14-2 and look dominant...lose the NFC championship game 30-20 to Jimmy's Cowboys who go on to win their 1st. It would have been interesting to see Marino lead this powerhouse against the new powerhouse from Dallas...another possibility at least.
1993
Marino hurt.
1994
Marino rebounds strong off Achilles injury....Niners are powerful and overtake the Cowboys without Marino and win it all...so with him I think they still win it all...Marino gets his 6th and final ring.
That's my opinion....I really think those 85-87 years were also strong possibilities as Montana struggled in the playoffs.