What I can suggest in Doflamingo's behalf is that he factually forced Luffy, or at least made him realize that avoiding his awakening was the best choice and Luffy is not dumb when it comes to fighting intelligence, therefore even post GK Doffy's AP is most likely quite solid. His speed was on point but he was being blitzed by G4, however it's comprehendable as he wasn't in his best shape. G4 was probably superior even to an healthy Doffy but that was time limited. Someone on YC3 level cannot afford that extensive massive level of potency and they would probably lose to Doffy generally, in standard conditions. I would not go as far as considering Doffy = King odds wise, but I would definitely easily place him above YC3 level, at least.