Rare Pair Fest

Chiming in to give a slightly different analogy, I'd argue it's like saying that Hamilton, Phantom of the Opera, and The Music Man are all going to be put together under "musicals" because they all feature people singing and dancing in them. NXT would be to WWE what "Eliza!" the hypothetical musical about the story of Hamilton's wife as a child, is--possible to consider it the same thing, though arguable. But Lucha Underground, WWE, and WCE have distinct casts, storylines, moods, even rules for the whole universe! There are dragons and time travelllers in Lucha Underground, for example, while a promotion like Ring of Honor wouldn't possibly have any whiff of the supernatural. I know it's a weird art form that doesn't seem to have any analogy that really clears things up, but putting them all in one fandom is not at all the best way.