I'm partly messing with you, but the truth is, which you may not agree with, but it's just the facts. The moment Rayleigh, a subordinate of the previous Pirate King, was shown to have it, the wheels were set in motion toward Zoro and Sanji eventually unlocking it.
There is no asspull because Oda never established any specific criteria for it. Rayleigh lived to make Roger King, and that was enough for him to be a Conqueror. Ace lived to make Whitebeard King, and that was enough for him. Sanji lives to make Luffy King, and that was always enough. This wasn't revealed to us in Chapter 1187. It's been there for a long, long time.