At this point in time, it's kind of like making a bet where you think a character will end up. If you think a character will end up in top tier, you might as well say so now, giving you the opportunity to say "I called it" later. I made the mistake of being too cautious with Joker: I thought he'd be high tier, but I was wrong, he turned out to be top tier! Of course, it's also very possible to overestimate a character. A DLC character being top tier wouldn't be surprising at all, we've seen it happen several times before, with Joker in Ultimate (and some say Min Min), Bayonetta and Cloud in 4 and potentially Ryu and/or Corrin as well.Seems a little early to be putting him in top tier with little to actually base it off of, but Smash community is going to Smash community I suppose.
Sephiroth is a very interesting case since a majority of top players seem to think that he's at least high tier. Has there ever been a DLC character where top players near unanimously agreed that the character was good and the character turned out to not be good? If not, then this would either be the first time, or Sephiroth will turn out to be good. My bet is on the latter.