Hard to say if they would have won, but I think they'd have done better. That was a tremendous Steelers team. But I do know that the 1975 team had one of Grant's best-ever defenses and Chuck Foreman had his best year, setting a then-NFL record of 22 touchdowns along with 73 receptions and a 1,000-yard season.
Would have been a lot of fun to watch, though.
Out of their four Super Bowls the Purple People Eaters played their best against the Steelers. Unfortunately for them the Steel Curtain played even better that day.