In my opinion, Liston was H2H No.2 in the second half of the '60s, while Frazier hadn't grown up yet; above Terrell and the others...
At the end of his career Liston was slow of hand and foot, and he had probably lost 20 percent of the speed and power in his jab. In his fight with Henry Clark his punching power appeared to have diminished. But he was still very strong and I think Frazier's pressure style might backfire against Liston. Sonny never fought a man as strong as himself and he was probably a lot stronger than Frazier. Plus he knew how to use rough stuff on the inside. Joe's managers weren't stupid; they weren't going to risk his bright future against a washed up but still dangerous Sonny Liston. Between Frazier and Jerry Quarry I like Quarry's chances better against Liston. Jerry was good against bigger men.
Considering Liston turned down a title shot against Ellis for a post championship highest payday, and multiple offers to fight Quarry we can safely mark the entire premise of this post as hogwash.
My thoughts as well, I've always thought Liston was one of 2 fighters that Frazier's style gives him no chance to win, Foreman being the other. Even though Sonny is long in the tooth, Frazier is playing to Sonny's strength attacking him head on throwing hooks. My conclusion is Frazier cannot get into a firefight with Sonny Liston and he 's not the mover and boxer that would be needed.