Huck by TKO. Let's see 'Jai' go toe to toe with prime Povetkin, a top HW amateur and pro. Until he does that he's getting TKO'd by Huck.
Currently Opetaia without a doubt. Even prime Marco Huck was beat by Glowacki who is far inferior to Opetaia's level, even if the Polish is really underrated his prime was pretty short at world level. The real question is Jai Opetaia will beat prime Mairis Briedis / Dorticos and I don't think he is superior than both in prime.
You're forgetting that the smaller in size heavyweights have always given Povetkin big trouble, whether it's Huck or Chagaev, or even Calvin Brock. Povetkin was a warrior who loved to go to war with giant boxers who preferred to keep their distance. When he faced heavyweight boxers of a similar build, he always struggled. Povetkin was a boxer who wants to destroy with his left and right hooks at mid-distance but without getting into close combat with someone who plays the same game as him.