Agreed, he had a multiple 5,000+ yardage quarterback for years, only had one SB. If Manning makes a better throw, then the Saints don't get the pick-6 and likely the Colts win that SB.
Same reasoning as for players like Aaron Rodgers, Brett Favre, etc. supposedly all-time great "elite" quarterbacks yet only 1 SB win each (though Rodgers could still get more). "Hitch your wagon to a star" is nice, but it's very difficult for one person, player or coach, to drag a team by the scruff of the neck to multiple SBs.
And just as a reminder, no coach has ever won a SB with two different teams, though Parcells came close, just something to consider...