If he fought all of them in real life scenarios, he might pick up a win, but in a fantasy matchup, I’d pick all of them to get to him. Marciano around 8 rounds, hacks him down using that endless stamina and pressure, Conn succumbs mentally and physically. Dempsey around the 4th, but if he doesn’t get Conn out of there, it could get interesting as Conn could then dictate the pace and possibly outbox him, I’d say Dempsey gets to him most times though. Frazier around the 6th round, he’s just too much physically from the off.