The title explains it all. We say things like PEDs don't give you skills, which is entirely true, but if they allow you train like a motherfucker and feel absolutely nothing and allow you to get in way better condition than the other dude. it does indirectly allow you to have a better chin.
Funnily enough the evidence isn't actually in boxing but in the UFC. There was a sweeping of both bodies and chins when USADA 365 a year testing came in. The dudes who were clearly cheating, because when you saw their bodies after USADA and it was nothing like before, their chins clearly weren't as good. they couldn't absorb punishment like they did before.