Joe Montana's career would have been even greater if he had been 4-3 in Super Bowls rather than 4-0.
If he had been 4-3, it would have meant that 3 extra times he would have won rather than lost in conference championship games. It is better to advance further in the playoffs, is it not?
To argue otherwise is the same as arguing that Brady was better / more successful than Manning in the postseason this year, since he lost the AFCCG rather than winning it, giving him no opportunity to even play in the Super Bowl.
consider a Super Bowl win a gold medal
consider a Super Bowl appearance with a loss as a silver medal (it should NOT be regarded as the worst of all possible season outcomes!)
consider an conference championship appearance with a loss as a bronze medal
consider anything else to be just a participation ribbon!
For his 14 healthy seasons, Montana amassed:
4 golds, no silvers, 3 bronzes
For his 12 healthy seasons, Brady has amassed:
3 golds, 2 silvers, 3 bronzes
Yes, IMO Montana's 4 golds, no silvers, & 3 bronzes beats Brady's 3 golds, 2 silvers, 3 bronzes
Imagine a Brady win in either of the next two seasons though. You'd have both QBs playing 14 complete and healthy years, and then:
Brady's 4 golds, 2 silvers, 3 bronzes clearly beats
Montana's 4 golds, no silvers, & 3 bronzes
Same deal if you imagined that the helmet catch never happened. Tom would have already surpassed Joe. But, alas, the helmet catch did happen.
Tom is closer to Joe IMO than Tom is close to Manning, who is several rungs below him.