Presuming that we're taking em from their primes at HW, Usyk will be 15.5 lbs heavier (Usyk from AJ 1 weighed 221, Frazier from Ali 1 weighed 205.5).
Have you ever seen Usyk "weared out"? This was also Usyk's 2nd fight at HW with a real contender that had a 38 lb. weight advantage. If Usyk was fully in-tune with his HW physique like he was in his last few fights he probably would have stopped Chisora.
I like Frazier by decision or maybe late stoppage. It'd be very competitive for quite some time wth Frazier slowly imposing himself over 15. 12 gives Usyk a better chance. Frazier would cut him off better than anyone has, work his body better than anyone has, and Usyk wouldn't have his usual stamina and workrate advantage. Usyk is a bit quick, classy and aerobic for the big guys he's faced. He's done a superb job against them. This is a very different fight.
What's the best weapon against a southpaw? Straight right. And Klitschko had one of the best straight right hands in the history of the division. He also had an ATG jab that Usyk may have problems slipping. Add to it that Wlad was one of the hardest hitter ever with an elite distance control and an elite clinch game. His killer left hook would also trouble a southpaw like Usyk. The mix between skill, power and size may be hard for Usyk to overcome. Especially since he doesn't have a kind of power that usually could bother Wlad.
I'd pick Wlad over Uysk, too, prime for prime. Imo, the most pertinent part of your post is Wlad's "elite distance control and elite clinch game". Arguably the biggest strength of both Usyk (along with his stamina) and Wlad (along with his power) is their distance control. Both were masters at it. The difference is Wlad is 3" taller with a longer reach. Watch him vs Haye, at the start of each round he adopts a distance relative to Haye so that the latter is just within his jabbing range, whilst Haye needs to take a step forwards to get Wlad into his punching range. Wlad then mirrors every step Haye takes to maintain that same distance. The rare occasion Haye gets his feet planted in his own punching range, Wlad clinches. Usyk has faster feet and far better stamina than Haye, but Haye has faster hands and is far more powerful. I think Wlad vs Usyk would be more competitive than Wlad vs Haye was, but still pick Wlad to win on points.
From stories I’ve heard Usyk embarrassed Wlad in sparring. I don’t take sparring stories all to seriously as sparring is about getting in shape and trying new things or tactics. But I’d take Usyk over Wlad
Idk how Usyk would handle an ATG swarmer/pressure fighter. Usyk reminds me of a bigger faster better version of Quarry and we know it wasn’t a particularly difficult fight for Frazier. Id pick Frazier here in a tough fight based on limited info.
Fraziers all wrong for the ferret, Frazier ****s him late stoppage hopefully so it doesn’t end Usyks career