At least Thompson usually had great recuperative abilities and really, outright superior durability. Ezra Seller's was extremely fragile in there. Guy could not take a punch, despite all his very real power.
Yh ive heard the rumour too, but it isnt true. There are pics of Both Tyson and Liston writing with their right hand.
Darroll "Doin' Damage" Wilson was a heavyweight who was also a converted southpaw. He could punch pretty damn well for a small heavyweight.
Frazier, Cooney, Dempsey, Morrison and Tyson all come to mind when you mention hard hitting left hand
These fighters were converted southpaws. HW Champs - James J Corbett , Jim Jeffries WW & MW Champ - Carmen Basilo HW challenger - Gerry Cooney Multiple World Champ - Oscar de la Hoya