You're missing the point, the issue isn't are there chars to pick from? Its are there any characters who can surpass the gravitas that Ultimate had. As much as people point to Sora, Steve and Dragon's Quest inclusion is also monumental. No remaining character can compete with that, the closest is Master Chief and its only him. Goku, Naruto and other 4th party characters can surpass that. And if we're going 4th party it makes no sense to only use one. Bring in as much money and attention as possible.
The point isn't missed at all: you are just biased. You have convinced yourself that because Sora was the King of Red Tape and earned the title of Mr. Impossible and he got in that no single character or combination of characters could ever reach this high.
Now, if you actually read from the list I linked, you would have seen there are way more characters than you are letting on about. Let me break it down for you here: you are implying the characters I'm about to list are not monumental enough to keep the hype train fueled and moving, and not all of these are on this list either, as it's a bit dated now.
- Crash Bandicoot
- Doom Guy
- Dante
- Rayman
- Phoenix Wright
- Reimu or anyone else from Touhou
- Waluigi
- 2B
- Spyro
- Stupid Fortnite character
- Ryu Hayabusa
- Actually impossible Mortal Kombat character.
- Tails
- Shadow
- Dr. Robotnik
- Dark Souls/Bloodborne character
- Any popular character from a popular fighting game (Chun Li, Akuma, Sol Badguy, Nightmare, etc.)
- Monster Hunter
- Kratos
- Anything from Valve
- Bomberman
- Raiden from Metal Gear Rising
- Saber from Fate/Stay series, if she even counts
- Agumon, if it even counts
- Any popular indie character (Shovel Knight, Shantae, Undertale character, Hollow Knight character, Cave Story characters, Celeste character)
Acting as if any of these choices aren't near or at the same level of hype is being completely unrealistic. Don't worry, I get you man: Joker, DQ Crew, Banjo, Steve, Sephiroth and Sora all in one game is really hard to match up with...but only at first glance, maybe second. However, look at this massive list I just presented that you can pick from for the future, and you realize that Sakurai has barely scratched the surface, even if he did grab some of the more incredible choices already.
There are also two other things you aren't considering: I don't think you are considering the real possibility of a Deluxe in which all of Ultimate's roster returns AND we get more characters, and I don't think you are considering the power of granting grass-roots fan requests.
I don't want to go into Deluxe territory here as I'm saving that for a big content moment, but I'll go into the fan portion here. You see, in that big list I gave, I purposely skipped over a number of characters. These characters are ones that aren't super popular and are more or less universally hype, but are instead ones that show that the creators are listening and that the power of fan demand is real, characters who only have a real chance because of the community pushing so hard for so long. These are your Genos, your Bandanna Dees, your Dixies, your Isaacs, your Porkys...these characters are just as important, if not more important, than your Steves, your Soras, your Chiefs. See, Smash has this thing where Sakurai and Nintendo have to balance out getting in very popular characters with granting the wishes of their fan base, and funnily enough it very rarely crosses over with Sora being one of the very few exceptions of being both incredibly popular and a massive request for years. Waluigi has morphed into one of the exceptions as well, being mostly a meme by most and wanted by hardcore fans at first, but building into this massive thing over time where he is genuinely a popular Mario character.
A lot of people would agree that Smash Ultimate ruined this balance, that it catered too much to the popular and not enough to the fan requests, and it's easy to see why: the DLC really only has three of these over 11 characters, being the DQ Crew, Banjo and Sora. The rest are either massively popular with a much smaller request, were never asked for in the first place, or fell off in request over time and now other characters are wanted more than them. When you add in how ARMS and XBC2 got characters in the DLC when people expected them in base where they would have fit much better, it really feels like the DLC wasn't handled as well from a request perspective as it could have been.
The base game hit numbers a lot better, giving us Inkling, Daisy, Ridley, Castlevania, Chrom, Dark Samus and K. Rool, but sadly three of these are echoes that could have been much more unique if the game wasn't rushed. So, considering only fully unique newcomer inclusions, Ultimate has Ridley, Simon Belmont, K. Rool, DQ Crew, Banjo and Sora in terms of listening to the fans who of been out there for years begging for their most wanted to get in. With this in mind, they could very easily focus on more of THESE kind of requests and balance it out with a few from that list I gave, and it would very easily meet or even exceed what has been set by Ultimate, especially if a Deluxe is in the works and no cuts are made.