While normally the Director idea of the game defines it, Smash is kind of weird as a crossover. Sakurai can say it's a celebration of gaming but Nintendo is the one who controls the purse strings and, consequently, who gets in. Nintendo, with the main roster, was willing to let Sakurai have one guest character (Simon) where they clearly let him go crazier for the DLC. As
@Garteam noted, it could easily just be a marketing gimmick.
And that's why I brought up the question. If Smash doesn't fulfill this "Celebration of Gaming" that people expect, how will they react. A lot of it is really based on what Nintendo wants. Nintendo was clearly fine ending Vol 1 with Byleth and starting Vol 2 with ARMS. I don't beleive people thing of "ARMS" and "another FE character" when you say "Celebration of Gaming." If the next picks aren't hype and are more Nintendo characters, would people be upset by that?
Since this is sort of related.....
One the question of the character after ARMS being a big character, the question would be why would they have not done that first? With Joker, they announced him 4 months before release, so it probably wasn't an issue starting with a big character even with delays. This is why I said in my post that there could be more Nintendo characters in Volume 2. It could even be the majority. It's more of a possibility than it was at the end of 2019. There is still hype characters they could add (namely Waluigi) but I don't think it would be Master Chief or Lara levels.
I think it's a fair point, My thought in writing the original post was more on what would people think rather than defining what Smash is. I say "Nintendo and Friends" because Nintendo isn't against adding other characters but there is a limit to what they'll allow. There was more Nintendo characters in Ultimate's base game than the DLC and the last two DLC characters are Nintendo so it may be the context of when they add these characters. My post was really focused on people's response. I don't think Max is alone in that people put Ultimate on this pedestal because it is Video Game All-Stars. If that doesn't happen in Vol 2 for whatever reason, what will these fans who have bought into this idea think.
I guess to expound of the last point: Nintendo fans can get invested in Smash because even with a lot of the guest characters, most of it is Nintendo. So if they add some doopy characters, it's not a big deal if they hit the highlights. But the group that see Smash as video game All-stars may not have the same relation with Nintendo and may have been brought into the fold with Nintendo adding more guest characters. With Smash Ultimate's DLC, it seemed like that was the case. But when the rug is pulled out, it's just a few guest characters and a bunch of Nintendo stuff. If you're not invested in the Nintendo stuff and they don't add the guest stuff you wanted, then where does that leave you?