AK was so good in his prime. I think AB would be able to get AK in a firefight late rounds though and stop him.
Everyone is asking how Kovalevs chin and body will hold up to Beterbiev's onslaught, but what about the converse; Beterbiev was dropped by Jeff Page and Callum Johnson, and Anthony Yarde had him hurt too. The difference between the two IMO is that Kovalev could land his power from range, and Beterbiev would have to eat a lot of heavy artillery to get into range to maul Kovalev. IMO if they fought 10 times I would back Kovalev to win 6/7 times out of 10.
Both at their best, I'd favor Beterbiev to grind him down to a late stoppage. Kovalev might be up on the cards when it happens, though. Or he would at least get out to a fast start. Peak Kovalev for the first six rounds was one of the great light heavyweights IMO, but his technique, guard, and footwork would get a bit more sloppy as fights progressed.