I understand what he's saying and he's right, Sephiroth was not discussed much prior to him getting in. If he was being talked about, it was probably in the context of the Seven Squares, but Sephiroth was never the focus of that conversation until after the fact when people somehow erroneously started thinking it was some comprehensive leak list, which it never was.
That doesn't inherently mean he was unwanted, just not seriously thought about. If presented with the hypothetical, I suspect many people would've been on board with it, just as they would be on board with another popular third-party from an existing series. It just didn't seem like an outcome that would be realized any time soon, and therefore was given all but no attention.
But having a support topic really doesn't mean that much. Hundreds of characters have a support topic. Really all it means is that at least someone out there wants the character, but that doesn't signify volume. It's true that we made very little noise in the way of Sephiroth, which makes claiming he was added due to our efforts a dubious proposition. He was added because he's Sephiroth, and that appeal is going to bridge a lot of communities, us included.
He was probably also added in part because of how well Cloud sold last time, and how much the character is played. Makes sense to return to that well.