Michigan's being downgraded here because people have been conditioned to think elite team = elite QB. It's the same reason the Heisman has turned into a QB popularity contest. Having the best, or one of the best, defense in football is one of the key metrics to winning a national title. I think there's a few teams (like 2019 LSU) that have an argument for THE best because they had everything AND an elite QB. But I think it's worth pointing out, again, that defense wins championships.
I'm not sure I buy the argument that this team wouldn't have beat some of the alleged "best" teams from past series. Michigan's route to this game was pretty incredible. Hell, people were predicting the Bama team they're now downplaying to win the title after they beat UGA. And they're only shitting on them because they lost to two other teams in the playoff.