The game CLEARLY states several times that Kingdom Hearts is a place.
The only stuff I remember is stuff like "the place where all hearts go" or something like that. But so what? My computer is the "place" where all my personal data goes, and that doesn't make my computer a place.
Nomura never said it wasn't a place either.
Don't give me "well nothing says I'm wrong" BS. Nomura also never said that KH2FM wasn't going to be released outside of Japan either, but we all know the answer to that.

So yeah, KH is pretty much confirmed to be an actually place.
If you're going to try and prove me wrong, don't use worthless, unmoderated, trash, wikia sites to do so.

This might seem tangential, but it purpose is to say that yeah KH is the integration of hearts but it can be a place at the same time.
Now you're just defining "place" in an abstract way. Either way, because KH is not a world, it doesn't have the walls that other worlds do.
Also, I assume that the In-Between Worlds are close enough to the Realm of Light that you can Gummi Ship it. TWTNW is closer to the Realm of Darkness thus the reason that the first time you go to it you must take a Corridors to Darkness/Dark Corridors.
And why would being closer to darkness prevent Sora from getting there by Gummi Ship?
Also, I was specifically talking about DTD and Dark Corridors in regards of travelling between the Realm of Light and the Realm of Darkness. I said "realms", I know but I wasn't really considering In-Between during that.
You're right that the DTD and Dark Corridors can get you to go from the Realm of Light to the Realm of Darkness. But what does jumping directly from Light to Dark and skipping In-Between have to do with what you are saying?

Wolf said that End of World is a place, not the DTD which is located therein.
You're not in End of the World anymore once you are done fighting Ansem 2, and the DTD is NOT in EotW.

I am pretty sure the two KHs never became one. There is a lot more evidence indicating two KH simultaneously existing than to theorize that the two became one. Basically, KH of Worlds is sealed away so Xemnas can't get to it, so he makes his own using the hearts freed by the Keyblade masters. I do not recall at any point there being indication for the seal locking away the KH of Worlds being broken or the two coming into one.
Xemnas' KH of men was ruined by Ansem the Wise's machine, but he still absorbed KH. The KH that wasn't ruined. The KH of worlds.