Which era would you like me to start naming fighters that would've beaten the hell out of Johnson. He was beaten a few times during his own era, K'oed twice before he had a total of 15 pro fights on record. So your "Nobody beats him" is totally wrong. And very silly.
Are you joking? JJ was a fairly big HW in his era. Modern era, even before the 2000s, he's a CW or very small HW (if he's in any decent shape). Many HWs before the 1950s would have been competitive or could beaten Johnson in a fight.
Outside of his ruleset? An overwhelmingly large amount of people. In it? You're right, probably no-one.
Foreman was supposedly invincible until he fought Ali.... Fury almost lost to Wallin... Marciano retired after Moore because he knew he was slipping and possibly headed for a loss if he kept fighting... Anyone can be beaten at the right time by the right person including Johnson (who was a darn good heavyweight)
Instead of going with the incredibly broad scope of looking for whoever would beat Johnson from across boxing history, let's just look at the implied matchup from the title in Johnson vs. Louis. I actually think this would be an intriguing matchup, if you replace Schmeling from his first fight against Louis with the Johnson of the Jeffries fight. Johnson did detect the holes in Louis's game that led to his defeat and bet heavily against him at the time. I certainly think that a serious, motivated peak Johnson would have a chance in this matchup, but it's far from a sure thing.
Personally I think Louis eats Johnson alive, Johnson would stand in the pocket countering feinting and parrying, but he isn’t mobile or fleet footed enough to frustrate joe, Johnson would have his moments early on, but Joe finds him and stops him between the 8th and 12th imo
You give him more of a chance than I do, personally I believe Louis destroys him, and Destroy him early if he fought the way that he did during his era.
