Dunno what BB or Landry would have accomplished without Brady or Staubach, respectively.
But we DO KNOW that with Staubach Landry won 2 SBs and lost 2 other SBs. He also got to a SB with Morton as his starter.
We also DO KNOW that with Brady as his QB, BB won 6 SBs and lost 3 others.
And we KNOW that with Favre and then Rodgers as his QB for 13 seasons Big Mac got to (and won) a single SB ... 11 seasons ago.
Finally, we know that Big Mac was 7-13-1 over his final 21 games in GB in 2017 & 2018 and that GB has gone 23-6 (24-7 counting the playoffs) in 2019 and 2020 since he was fired.
Definitely their levels of success have differed with their great quarterbacks. The point is that with just a few exceptions, any coach you are going to name who had Super Bowl success also had a great quarterback. So if we're going to say McCarthy couldn't do it without Rodgers, then he's among some pretty good company there.
In his 13 years in Green Bay, McCarthy's teams won the NFC North six times and made the playoffs nine times, including reaching the NFC Championship Game four times. So his success isn't shabby.
We also know that during his last two seasons in Green Bay, Aaron Rodgers had some pretty bad injuries, playing in only seven games in 2017. Even in 2019, Rodgers wasn't quite the same as he had been (actually having a worse year in some aspects than he did in McCarthy's final two years), but Green Bay has done a much better job the last two years of putting a good defense together.
In fact, if there's one area that concerns me with McCarthy is that I think he's another coach who doesn't value defense as much as he should IMO.