Nintendo is a much different beast compared to Capcom when it comes to character picks. It's not just that Nintendo has arguably alot more popular characters, but Nintendo has too many "unique main-pick" characters to be able to simply pick "out-there unique picks". Mario, Luigi, Peach and Bowser are easily "the Top 4" when it comes to Mario characters and you can't just go, "Why not pick a couple of characters besides the main 4?" Because these are arguably the characters people really want to play as, especially if it were to be something along the lines of Vs. Capcom.
And the uniqueness excuse can't work with them because they have so much material that you could make multiple unique versions of each character. You could easily make 10 versions of Mario, all with completely unique movesets. The unique and creative moveset aspect cannot be used to explain why a character like Ashley from WarioWare should get over Peach. Peach has the main Mario games, she has the spin-off Kart/Party/Sports games, she has the RPG games, she has Super Princess Peach, she has Princess Peach Showtime, she even has the Game & Watch Gallery games. She has 5 times the moveset material than 3/4 of the cast of Smash Bros.
This is part of why I keep saying that Nintendo is a lot harder to do Capcom-style picks because of how much of an impact Nintendo's main series and Smash Bros. If something like Vs. Capcom happens, most people will prioritise to see their favourite characters get in, especially the ones they've been dreaming of seeing interact with each other.
- People want to see Mario, Luigi, Peach and Bowser fight against Megaman, Protoman, Roll and Dr. Wily.
- Link, Zelda and Ganondorf are The Triforce of Zelda characters. Smash fans may be annoyed at the lack of characters outside those 3 in Smash, but if we were to get a new crossover game, people would still very much want all three to appear.
- People want to see their favourite Nintendo characters like Isabelle, Agent 3/Inkling, Samus, Donkey Kong, Fox McCloud, Wario, Captain Falcon, Ness, Little Mac, Marth, Lucina, Pit, Palutena, Kirby, Mewtwo, Pyra & Mythra and whatnot fight against their favourite Capcom characters like Ryu, Chun-Li, Dante, Zero, Morrigan, Strider Hiryu, Amaterasu, Arthur, Jill Valentine, Wesker, Phoenix Wright, Mike Hagger and whatnot.
Like some people will be open to surprise picks, but most people want to see their favourite main characters from their favourite series interact with each other first and foremost. People talk about the lack of more minor picks, but it doesn't help that the majority of characters in Smash Bros. were heavily favoured by their communities before they appeared in Smash Bros. Yes, even Corrin and Byleth, much to some Smash fans' chagrin.