So in summary, this is what I think happened...
-"Insiders" were fed misinformation about the roster, mainly things about Incineroar and Steve. Whether they knew it was misinformation is anyone's guess.
-This was the red herring to lead us away from leaks speculating on the real roster because Sakurai wanted the real roster to sound like a pipe dream of "never-evers"
-Eric Bricard brought his grandkid into work one day. We've seen the ACP-PLV building and it's more than large enough to give a tour of. Grandkid (who I believe is also named Eric Bricard) snapchatted something he shouldn't have to his friends, believing it wouldn't actually go anywhere, which turned out not to be the case because his friends got ahold of it.
-ACP-PLV has refrained from commenting officially because they simply cannot do so, any form of comment would basically further spill the beans.
-Many youtube channels that were all about discussing certain leaks in the past have clammed up about the Grinch leak, leading me to believe that Nintendo has told them to clam up about this one and dismiss it as hard as they can.
And TBH, it's this last point that pushed me into team real. Remember, these youtubers are basically throwing ad revenue away by NOT talking about this leak, and given that this is the most news SSBU has seen in a while, they should be absolutely eating this stuff up like starving dogs.
The only explanation as to why they aren't is because Nintendo has told them they won't get any early copies or whatnot if they don't work as hard as they can to push the leak out of the public eye, which is ironically having the opposite effect for many people.
The only other thing I can come up with is a literally insane theory that Sakurai planned this whole thing to reignite the hype fire leading up to the release, but I doubt it because he'd be giving away the very best parts of what should've been amazing surprises. If this leak was faked by Sakurai himself, he'd have shown the banner with no one but Ken and Incineroar added.
So yeah, I think it's real, and all of the "insiders" and youtube channels who used to love to talk about fake leaks suddenly trying to push this one away is what finally convinced me.