Marino not winning a championship does not undercut his greatness in any way except through the eyes of some fans (who generally don't know what they are talking about). It's a rather lazy argument to make and neglects to look at the whole picture (just as somebody who makes the flipside argument by suggesting multiple championships makes somebody greater). This isn't true in football. Guys have their responsibilities. Because of the nature of the game, any faults in football are harder to overcome than other sports. In basketball, just two guys can make a big difference and players always play both sides of the floor. In baseball, poor pitching can be difficult to overcome. But, poor pitchers get pulled frequently and players play both sides of the plate. In football, offensive lineman must block. Backs must block, receive (depending on the type of ffense), and run with effectiveness (which goes back to blocking). Receivers must get open and run correct routes (and catch the ball) in addition to blocking when necesary. Tight ends must block and catch effectively when called on. Quarterbacks must mitigate defenses by correctly reading them, audibling when necessary (and when allowed...Jimmy Johnson never seemed to get this), delivering the ball effectively and on time in a tight windows. Defensive players all have responsibilities from reading offenses, making tackles, making plays on the football, forming effective pass rushes, etc. Guys aren't playing both sides of the ball. There is leadership, which can take many forms. Good, even great, leadership cannot overcome everything. If you look at the 2007 Dolphins, Jason Taylor and Zach Thomas had very good leadership qualities and played great. Miami was in several one-score games. But no matter how good the defense played at times, it could not overcome an offense that desperately needed life support. In many ways it was the exact opposite of almost the entire Marino era. The Defense got old and fell apart quickly after 1982. Even Bill walsh remakred after Super Bowl 19 how great of a job Shula did with with the team given it's limitations on defense (Walsh said a lot of Miami defense even holding together that year was done with smoke and mirrors...his words, not mine). walsh wa sconfident after pre-game warmups that the 49ers could score and score often. He only worried about Marino.
The Dolphins defenses gave up an average of 44 PPG in 10 Miami playoff losses with Marino. Your argument about it being impossible to win championships without a total team effort is spot on. But I don't hold it against Marino given the circumstances in Miami. During his career, the only HOF players Marino played with were Stephenson (until 1987) and Jason Taylor. Taylor came to Miami very late in Marino's career and didn't turn into a major force until after Marino retired (Taylor was good early but then he exploded) . Thomas will likely get in one day. Even many Miami's "good" players were second-tier compared to a lot of other "good" players on other teams (guys who were standouts but will not get HOF consideration). Frank Gifford once said that he "equates stupidity to anyone who says Marino not winning a Super Bowl takes away from his record". By "record" he meant career and accomplishments.
