Frazier-Quarry I stands out for me when you're talking about two heavyweights whaling away with body shots. Frazier was the superior but Jerry packed a terrific left hook to the body, too. And while on the subject, let's not forget George Chuvalo.
H2H makes this sort of weird? Tunney and Toney were a million times better then a lot of heavies as boxers... but would Lennox being Lennox make him rank higher? - Despite being nowhere close to those guys. I'd say overall technically speaking it'd be Marciano? Dempsey and Louis those three are pretty close, followed by guys like Tunney, Toney, Charles, Moore and other smaller guys with skill - I think Evander is in there somewhere on the lower end... looking at say Norton... as a boxer he's as smart as a Labrador next to Toney but in the ring it'd be a lively discussion... am I meant to factor in stuff like that or are we talking about the actual art of boxing across the weights?
The mistake you're making here is believing power is so relevant to body punching.... it's placement! It's why Toney could stop Holyfield whilst say giant guys like Rahman, Lennox and Valuev couldn't make a dent. Foreman swung wide and hit wherever he could, that's not what you do when you're trying to break a guy down.... it's precision to stop someone from body work... watch Mustafa vs Pops. Usyk would literally be an alien to Foreman who never fought a real deal Southpaw, Usyk on the other hand is better then Jimmy Young and used to "big" (he'd be a cruiser today...) dummies by now.
I'm not sure Usyk is even the best bodypuncher in the division. Kabayel and Gassiev stop guys with bodyshots.