Notre Dame and Alabama have identical yards per play given up, 10th in the nation, Georgia is 20, LSU 39. Yards per carry allowed is Bama 17, Notre Dame 40, Georgia 54, LSU 66. Passer rating against LSU 8, Notre Dame 9, Alabama 10, Georgia 22. Yards per attempt allowed Notre Dame 6, Georgia 8, Alabama 12, LSU 18.
S&P+ is opponent adjusted so it's not about playing cupcakes or bad offenses. I imagine if we watched every Georgia game, or LSU game the same way we watch Notre Dame, and viewed Notre Dame from afar, we might look at it different.
It's hard to imagine Bama isn't #1 in everything though.