How good was Sonny Liston

[[censored]]

I was able to catch the Clay (Ali) - Liston fights today on EPN classic which was a treat. However the coverage did not really detail how big if any an upset that was. I think it mentioned something like 8-1 against Ali but it was not clear if that was due to ALi being unknown of out of respect for Liston. Was Liston considered a "great" champ or was in more of the Larry Holmes mold as a champ inbetween great champions (Ali and Tyson for Holmes; Lewis and Ali for Liston)? What more recent boxers would he compare to?

Liston record