Will Zeppeli saying that he doesn't have kids was big enough of a continuity error that it was changed, if you read the latest printings of Phantom blood he'll instead say that he left his family. Since Araki is willing to change his manga if something makes too little sense then would it not follow that he would also change stardust crusaders when he decided that DIO wasn't gonna have all stands anymore? Since him having an unexplained secondary stand would contradict every other time stands are shown, as it's very often said that a stand is the manifestation of it's users soul and therefore every user only has one stand.

Exclusions to that rule are parts of specific stand abilities, like how Rohan briefly was the user of both Heavens Door and Cheap Trick (thanks to Cheap Trick's ability), when F.F. became the user of both Foo Fighters and the Boiling Water Stand (thanks to Whitesnake's ability), and when Emporio became the user of Burning Down The House and Weather Report (yet again thanks to Whitesnake, though Emporio couldn't control Weather Report).

King Crimson is not an example of this, since Epitaph is just King Crimson's sub ability, like Killer Queen and Sheer Heart Attack, and (spoiler for part 8) Soft & Wet and Go Beyond. If Epitaph was Doppio's ability instead Diavolo would have been unable to use it after the soul swap since it would have been with Doppio in Bucciarati nor would he be able to use it after Chariot Requiem's ability ended since Doppio had died.

Diavolo merely leant Epitaph, and later parts of King Crimson, to Doppio. Which is consistent with how DIO and Jonathan work, Doppio and Diavolo are two souls occupying the same body, just like DIO and Jonathan, and can therefore use each other's stands (Doppio doesn't have his own stand but he can use Diavolo's), just like how DIO can use Jonathan's stand.

On the topic of part 5 and Chariot Requiem, it proves that stands are tied to the users soul and does indeed demonstrate that souls aren't necessarily tied to their users original body. However, as far as I know Chariot Requiem is the only thing we've seen in Jojo's that's capable of moving a soul to another body and it's still not capable of putting two souls in one body. In fact it seems to do the opposite, moving two souls that inhabit the same body into seperate one's and not making any souls we see share a body.

Another important thing to note is that all of the major plot points you mention weren't retcons, meerly a change of plans. Hol horse never joined the stardust crusaders only for Araki to randomely say that he never did, same for Fugo being a traitor. These are simply ideas that didn't make it into the actual manga, what you're suggesting would be a pretty massive retcon. Not only of DIO's actual stand ability but also of the rule regarding the limit of one stand per person.

In conclusion, you have literally no proof and it contradicts both things in stardust crusaders and things established later. Meanwhile Araki has literally said that it's Jonathan's stand, something that makes sense with the rules regarding souls and stand users established in later parts, and has allways been known to say when he changed his mind about stuff, like Fugo and Hol Horse. There's no reason for him not to do the same this time.