In the regular season, he was good enough to beat the '85 Bears. However, in the post-season, he couldn't beat the '85 Patriots - at home - in Miami - and was badly outplayed by the "great" Tony Eason. No defense? He was drafted by a team that was just in the Super Bowl. Do you think David Woodley's passing got them there or was it the Killer B's defense? Woodley took the Dolphins to as many Super Bowls as Marino in far fewer seasons.
Marino had two INT's and a fumble, but others contributed to the defeat as well. Tony Nathan fumbled on Miami's own 18 early in the first quarter that led to an NE FG.
With the score 17-7 NE, and about 1:04 left in the second quarter, Fuad Reveiz missed a 31-yard FG.
Then, with the score 24-14 early in the fourth quarter (and Miami trying to mount a comeback), RB Joe Carter fumbled the ball at the Miami 45. The Pats recovered and scored a TD to make it 31-14 with about eight minutes left (all but putting the game out of reach).
No running game? Another myth. Plenty of examples of teams that won a Super Bowl with far less of a running game than Marino had in Miami. The greats are supposed to elevate lesser talent. Brady won 4 rings handing off to Antwain Smith, Sony Michel & Leonard Fournette. Manning won his with Joseph Addai & CJ Anderson as his RBs. Mahomes has had Damian Williams and Isaiah Pacheco. Montana won with Earl Cooper. Rodgers had some guy named Brandon Jackson.
Brady also won with Corey Dillon once, and he lost when he had one of the best offenses ever. Manning won in 2015 because he had one of the best defenses ever (Marino never had anything like that around him). Montana won because they added three first-round talents in the secondary along with Hacksaw and Fred Dean. As for Mahomes, I won't address him because he is overrated, and the NFL fixes it so bad for the Chiefs. They aren't a real champion.