You cherry picking our worst two games is what losers do. Decent opponents we played: Iowa, Stanford, Michigan, Penn State, Wisconsin, Duke. Points allowed per game 20.33. That would put us at 18th the country if we allow all the other teams in the country to include all there games. Decent teams you played Clemson, Navy, USC, Temple, Pitt, Stanford. Points allowed per game 27.83. That would make you 75th nationally.
Oh, and I actually watched all the Northwestern games and several Notre Dame games so I could probably tell you whether our defense is elite.