Agreed. It's not like Ali didn't fight several Bermane Stiverne level fighters in his career! Leon Spinks anyone? Hell, guys like Richard Dunn and Chuck Wepner are a step below. These kinds of hypothetical matchups are worth discussing. Sure, Ali almost certainly wins, but it doesn't mean it can't be examined. Under what conditions might the upset occur?
I dont think Ali could outright KO Stiverne. He is very tough and with a granite chin. TKO on cuts maybe? Stiverne was never the best at slipping punches, so he would probably eat the jab all night. If not a stoppage, then Ali by a lopsided UD.
Ali would have schooled him pretty bad. Nowadays the heavyweights are heavy because they ate too much not because they are necessary bigger.
Stiverne by brutal ko in the 6th, after teaching a boxing lesson. only Ali's chin holds him up to that point. Too fast, too strong, too smart for Ali.
Lasting 12 rounds against Wilder ... is as good as a win against any of the (other) HW greats in my book.