Yeah, that's the usual argument. No disrespect intended, but it's lazy thinking. Are Jeff Hostetler, Doug Williams, and Trent Dilfer also better than Marino because they each won a Super Bowl? You have to take into account all sorts of other factors, especially the quality of the team around the QB, but also the coaching, ownership, the era (e.g., PI penalties), and how many healthy years he played.
I'm not dissing Brady (although I despise his Marcia face), but having watched both him and Marino, there's no question, to me, that Marino was better. Put him on Brady's teams, let him play there until he was 45, and he would have won more championships.