I don't think Smash was ever meant to be that. It was originally just a fun crossover game with a bunch of new and old Nintendo characters. It wasn't until 4's DLC where they started going heavier on third party characters. Even then, the cast is majorly from Nintendo IP's. As for it being to close too Three House's release, this has been happening since Melee. Roy, Greninja, and Corrin were all added relatively close to their respective introductions.

But consider this: The people who wanted character A to be in Smash and the people who aren't satisfied now that character A is in Smash and want character B to get in might not be the same people.

We have a tendency to personify large groups like fanbases like they're a single individual with clear-cut opinions and desires. Obviously that's not really the case, and especially not with the Smash fandom, which is not just massive but is very diverse since it's such an enormous crossover game.

(Plus, as a casual observer, I've noticed getting really hyped about things is half the fun people have with this game. Of course they always want more. That shared excitement is addicting, and it brings people with the same enthusiasm together.)