You really dont get it, lol.
If Luffy was the reincarnation of Joyboy, Zunisha would hear Joyboy's voice the whole time.
Luffy's voice had to disappear for Joyboy's voice to take over and return for the first time in 800 years.
What if Luffy never ate that specific fruit? Joyboy wouldnt return. Reincarnation doesnt work like that.
If he is the reincarnation of Joyboy, the awakening of the fruit is completely irrelevant.
It means Joyboy's will has taken over his body. The only question is what's the source - DF or the hat.
You remember that we literally saw Death coming after Zoro?
His return has been foreshadowed and I bet he is driving Kaido into suicide, so he can finally take over.