In a sport with over 100 years of history, and probably 10's of thousands of competitors, I find it hard to believe that anyone on a top 100 all time list could be classified as mediocre.
Douglas had skills . I would put him in the same class with Greg Page, Tua & Riddick Bowe. If they had bothered to get into top Physical shape. thier respective boxing legacy's would have been much better that what they are.
He could reasonably be in the top 50, was the undisputed champion even if for a brief time, has one of if not the greatest win, and also beat past and future champions.