Parker isn't a huge heavyweight by any means but at 6'4 270 lbs he's still way too big for Beterbiev. He'd hurt him badly imo.
I would make Parker a slight favorite due to the substantial size differential. But, it could be reasonably competitive due to Beterbiev's skill and toughness differential. But, Beterbiev's proclivity for mixing it up would likely be his undoing. I would be more inclined to pick a guy like Roy Jones over Parker. His speed and movement would make Parker look silly.
He didn’t make a move at HW due to his physical dimensions. Why are people always trying to belittle LHW or CW fighters who only fight at those weights? We have weight classes for a reason. Most HW fighters are fat and useless. The talent pool is smaller than any other weight class. Because the amount of people over 6 foot 2 to 3 who can fight is very small in the general population. A lot of chancers there and it’s not the elite division based on number of fighters, but at the top it pays the best.
In light of the fact that most of the boxing world believes Beterbiev was beaten by Bivol, a natural SMW who fights at LHW, I think it is time to stop these fantasy match-ups with heavy. He is almost 40, and I am not saying that he could not have done any better under different circumstances, but the fact is that we will never know. He boiled down to LHW for most of his career, blew it in his big fight, regardless of what the cards said, and now he's most likely headed down.
Usyk, AJ, Dubois, Parker, Wardley are all on superb physical condition. So were both Klits. Sure there are the Ruiz, Big Baby of the HW division but they are few slobs in the top ten. Of course Fury comes to mind but he just doesn't have the type of body that will get six pack abs.
Yes the upper echelons are the only lot that are in shape. The vast majority of HWs though are just glorified punching bags and the talent pool is low so the criteria for entry is lower. This isn’t the case at the lower weight classes. If you want to identify the division with the biggest talent pool it’s MW and either side of that.