I think everyone needs to understand the fact before arguing endlessly over it, The point is, it had reasons to be assumed inside the U7, more than just one, and it's only because it was introduced before the time multiverse introduced in dragonBall, keep in mind that it being introduced before the multiverse wasn't the reason but it created several reasons. Now that multiverse is properly established and it has evidence for not being a part of the universe and usual spacetime itself, those reasons has turn to dust. Now it requires evidence for it to be a part of the Timeline, the reason can't be same that has been discarded by the lore or manga itself.