I fully agree with your assessment. The game had a great trailer, a groovy vibe, and was right on the back of the Mario movie. It would have been almost exactly as successful with the classic turn-taking multiplayer experience.
It was cool to be able to play with friends and see the ghosts of randos, but it was a minor novelty, not a major selling point.
If this game is to Nier as Lies of P is to Dark Souls, I'm here for it.