I have no doubt this is a retcon asspull, but I wonder
when Oda decided this.
Did he already have this in mind since the Gear 4/Rayleigh flashback? Maybe Rayleigh knew about Gomu Gomu no Mi/JoyBoy connection, and helped pushed Luffy to awakening.
Kaido already mentioned second last chapter that Snakeman was already doing non-rubber thing. Maybe Luffy was already partially awakened.
This would mean "Gear 5" is just the completion of his awakening.