Let me ask you all one simple question.
Think about this really hard, okay?
If what you're saying is true.. and Luffy is NOT a reincarnation of Roger or Joyboy, then why do Roger and Luffy share the ability [The Voice of All Things]?
What is the probability that they would both develop that extremely, extremely, rare ability? Can you explain it.
My explanation for that is that Luffy and Roger share the same soul. Their soul originally comes from Joyboy and that's why they all have that latent ability. Luffy shows it in smaller ways than Roger did, but that's only because Luffy hasn't developed it very much yet. You see glimpses of it developing in him already, though. Like how both Luffy and Roger could hear (1) the Sea Kings and (2) Zunisha. I will have to look for more instances of when he's applied this strange power to provide examples, they're rather difficult to find because they're so rare to see and there's a lot of content to sift through.
But think about that..... how the hell could Roger and Luffy both have [The Voice of All Things] without being reincarnations of Joyboy?
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I need to point something out here.
On the internet... it's believed that Oden, Momonosuke, and Princess [Shirahoshi] also have this ability [The Voice of All Things].
This is a LIE. They do not actually possess the ability to hear the voices of All Things. They can only hear the voices of very specific things, actually. For example, Shirahoshi can ONLY hear The Sea Kings or other forms of sea-life. I believe the same is true of both Oden and Momonosuke, and they can also ONLY hear certain forms of life like Zunisha.
The difference between those people and Roger or Luffy is simple. Roger, and Luffy can actually hear the voices of All Things. That's why they could hear both the Sea Kings AND Zunisha (but, they could not talk!! Not yet).
So, the difference is some people who used a similar ability are being overlapped with people who possess a greater version of that same ability. The thing Oden, Momonosuke, and Shirahoshi do, is DIFFERENT than what Roger and Luffy do.
Oden, Momonosuke, Shirahoshi = Can ONLY hear some voices.
Roger and Luffy = Can hear ALL voices.
Conclusion, ONLY Roger and Luffy have demonstrated the ability to use [The Voice of All Things]. If you wanted to say Oden, Momonosuke, and Vivi have something.... they have [The Voice of Some Things]. It's not the same ability, at least not on the same degree of power. They have a lesser ability compared to Luffy and Roger.
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https://onepiece.fandom.com/wiki/Voice_of_All_Things
This website gives the misleading notion that they all possess the same ability, and gives the reader the idea that Oden, Momonosuke, and Shirahoshi all possess The Voice of All Things.
The Voice of All Things means commanding everything around a person.
It is NOT surprising that the Sea God Poseidon can command any sea creature or the sea environment itself.
It is surprising that Oden, and Momonosuke can command creatures, but it's likely they are actually reincarnations of some kind of God just like how Shirahoshi herself is. This is what explains the latent powers. The reincarnation aspect. So they too can command some kind of creature in some kind of environment.
However, I think you'll see later they can't command creatures of another environment and also may not be able to hear them either. Unlike Luffy and Roger, who can hear anything from any environment (and eventually will be able to command them all too).
Think about it. Really think about it.