John Sullivan the first heavyweight champion, was he really that great?
No he wouldn’t last against the guys you mentioned, Sullivan was more of a MMA fighter than anything else, he grabbed and held his opponents down then punched the daylights out of them, he wasn’t that big and not particularly fast nor strong, he was more of a street brawler kind of guy (a mini kimbo slice) but in today’s world under modern boxing rules he would loose against a lot of guys, moreover he only fought white people so it is even harder to judge him (jeffries and corbett in their primes actually did fight a few blacks) he was one tough S.O.B though and i wouldn’t mess with him lol.