Top 10? Just a gargantuan size difference between him and some of guys up there. We'd have a real life example of how someone like Rocky Marciano would fair in this era.
He wouldnt rank in the top 10. Hes too small and he isnt elusive. Hes there to be hit. Even Dillian Whyte would knock him out.
He has most important thing that would scare away most of the HW. Pure, raw power that would destroy any of them. If Canelo can spar with Sanchez and don't get KO'ed, what makes you think that Beterbiev don't have a chance against any of them ? But first he has to beat CW champions. Someone like Makabu
When you look at the prerequisite to be sucessful when you move up division, it's a common denominator : speed. Ultra speed. Beterbiev ain't Roy Jones, Pacquiao, Canelo or Mayweather. He won't move up heavyweight and also he is 37 years old and speed is the first thing affected by age.
Beterbiev is getting old, but just off his vast ring experience and most of the current heavyweights lacking ring experience Beterbiev wouldn’t have a hard time becoming a top 10 heavyweight. At his current age I could see Beterbiev beating guys like Hunter, Dubois, Kownacki, Gassiev, Yoka, and Parker.