I think even that version of Duran (2 days shy of his 46th birthday) would beat badly faded Kovalev, who seems to have ZERO punch resistance and terrible stamina nowdays.
Duran was far too slow at 46 to get past Kov`s jab that kept bouncing off Canelo`s guard, Kov was scared of throwing his right hand because of Canelo`s counter hook, but Duran`s counters were very slow at 46 and he`d be even slower at 175, Kov still has power and the first power shot would knock Duran out, his reach would be too much also, Canelo would have stopped a 46 year old Duran a lot quicker than the time he took to stop Kov.
At that point Roberto was just too slow and stationary. He would not be able to close the gap.Kovalev would just outpoint with the jab in a boring fight.I would actually give that version of Duran a better shot against Canelo