I would say very very good chances. Footwork fight and Gene turns him all night and Mercer does not let his hands go if a guy is out of range. It would help a bunch if he had the refinement to throw while moving those feet. And against a Tunney one step won't do it. It would have to be 2 or 3 steps and Ray would just be operating from a different timezone.
If Jesse Furgeson could outbox Mercer so could Gene Tunney but Ray could be dangerous and he was durable. Tunney on the move and work rate and stamina make it hard for Ray in rounds 10-15 but Gene WUD 15
Mercer had slow feet I could see Tunney dancing rings around Mercer and winning a decision. But it wouldn't surprise me if Mercer caught Tunney at some point and knocked him out. If a past it inactive Dempsey can have Tunney on the floor for 14 seconds it wouldn't be out of realms if a focused in shape Mercer caught him aswell. I'd probably make Tunney the favourite but I wouldn't bet on it Mercer is alot bigger and hits hard enough to seriously trouble Tunney.
The Mercer who fought Lewis probably takes it. Otherwise, Mercer likely loses a clean decision. Tunney ain't knocking him out. A prime Mercer probably takes a 10/10 puncher unloading a 20 hit combo and landing most of them to knock down. His toughness was unreal.
Mercer's only chance to win is the cliche,,"Punchers chance" which I think amounts to being a 4 or 5 to 1 underdog
Tunney's estimation at heavyweight is the single most laughable aspect of this board, which is saying something. Mercer would walk right through Tunney, slaughter him.
Offend away. Tunney has the flimsiest heavyweight resume of anyone I've ever seen ranked in the top 20, let along top 10. There is no "there" there.
All the intangibles and style matchups favor Tunney. The fighter with elite 15 round plus stamina - Tunney The always prepared and in shape fighter - Tunney Style wise Tunney was a good mover, an excellent boxer, and had a strong jab. All issues for Mercer. Mercer looked his best in two losing efforts, his career best against Holyfield and his war with Lewis that he arguably won. He looked pretty bad against the easy to hit Morrison until Morrison gassed, he looked beatable against Damiani too, until an unorthodox punch broke Damiani’s nose. Then let’s look at the Ferguson fights, Ocasio, old Witherspoon, Holmes schooling, Ray was quite beatable. What he has in his favor is his size. Is he just too big and heavy for Gene. Could he catch Gene? I don’t know - two trains of thought on the matter. But Gene was the more consistent fighter, the better fighter and the more accomplished fighter.
The Fighting Marine's Ring IQ, footwork, defense, and accuracy would be decisive. Mercer, a very good and strong fighter, would have faced a great champion. Skill, style, and fighter value can prevail over a 30-pound difference (see Usyk- Fury), so I say Tunney is comfortable on points.
He doesn't deserve to be ranked in the top 20 heavyweights all time but Mercer wouldn't be anywhere near that level either.