I was just watch a Khaosai Galaxy highlight and thought he has to be the hardest hitting southpaw I've seen. Name some other great left handed punchers.
Both Tyson and Liston are rumored to be converted southpaws. (When I say "are rumored" I mean I read that speculation somewhere semi-credible and can no longer recall the source.)
Don't know about Mike ... but here's an old SI article about a sparring partner, Ben Skelton, who sparred with Louis, Charles, Walcott, Liston, and Patterson, who heard the same as you about Liston ... It's a good read https://www.si.com/vault/1962/09/24/624848/a-sparring-partner-looks-them-over
A few world class punching southpaws in chronological order.... Lew Tendler. Jimmy Carruthers. Marvin Johnson. Antonio Tarver.
Probably the single hardest hitting cruiserweight of all time. If only he didn't have such atrocious durability and stamina... That exciting win over the never say die Carl Thompson though... oh boy.
Seems like some of Liston's amateur records in the early 50's might reflect if he ever fought as a lefty.