What do you consider a "large role" exactly, because the games listed were the newest Mario game, the newest Zelda games, the newest FE game (which usually gets something, mind), Pikmin 4 and Xenoblade 3 when both of their series have seen huge growth on the Switch...
I mean.
Mario Wonder is definitely old enough to get a stage, and what else can you do with it?
TotK can get a stage and even a character. It's been announced while Ultimate was still getting DLC, the Zelda team keeps Sakurai up to date between different projects (they even designed Sheik for Brawl while TP was in development) and it's official that TotK has been content complete for a whole year before release. They spent the last year just debugging.
Fire Emblem operates the same, so they probably can add Alear if they really want to, but honestly I don't think that all that many people would be disappointed if they sit this one out.
Pikmin 4 can get a stage. Oatchi becoming a character is a bit of a long shot regardless of everything.
Xenoblade 3 gets the short end of the stick, but... it happens. Mario 3d World, Tropical Freeze, every single Metroid Prime past the first one, a vast majority of post-SNES (!) Kirby games, most non-3d Zelda games, Xenoblade X, Radiant Dawn, Starfox Adventures, TTYD... I could go on, but anyways... they all got skipped over when it was their time. It just happens. And even then, they might have reserved a spot for the XB3 character like they do for Pokémon anyways.
I'm not saying that the game will specifically be delayed to account for this and that, but I am saying it would be a stark break in routine for next game to be missing the last few years of the Switch, where we'd still picking up previous generation slack through DLC and into the future of the series. I just don't think 2021 gives us that much wiggle room. It could happen, but I'd be disappointed in screwing with this comfortable pace the series has been at for almost 20 years. If it ain't broke, why force it? A roster decided in 2023 can see a 2026-2027 release and that would be perfectly in-line with Smash's usual shtick.
The last few years of the Switch wouldn't be totally missing. It's just that maybe they'd get 1-2 characters instead of 90% of the newcomers. Hardly a big deal. That was the case for Brawl too, and a vast majority of the Ultimate newcomers wasn't topical either (I see no reason why you wouldn't count the 3rd party characters) and it's the most successful Smash game ever.
Point being, they might feel like releasing Smash early is more important than it having a ton of characters from the late-era Switch games - which seems fair enough to me - and that's probably what happened if Sakurai's project from 2021 is indeed Smash... which it kinda has to be imo.