You must think millions have ridiculous thoughts then. And yes, I know those millions aren't directly saying "**** ATs/spirits/etc, all my homies hate non-fighter representation", but they're still mainly getting into games that got Smash fighters instead of ones that got ATs/spirits and consuming content primarily focused on the fighters, and then there's those who play without items therefore making fighter representation even more important.
No, the mindset I'm talking about is treating them as an insult. That's not the same as preferring a bigger role for your favorite character.
So I'm not remotely talking about the mindset you're speaking on. When you're treating fanservice as an insult, then it's actually ridiculous. When you simply aren't happy with something else, it's actually reasonable. Nobody should be happy with something if it's not what they want.
They're completely different mindsets. Reality is, not all will get some big role as another. That's just life. That's why they're still there so fans actually get cool content. Cause otherwise the game would frankly suck if it had only playable characters, no costume references at all, stages(but absolutely zero bosses or cameos. Yes, that means no Master Hand, since you couldn't play as him), no items, no trophies/stickers/spirits. Literally zero NPC's. That doesn't sound like a good game at all. It just doesn't work. Smash 64 did only decently and there's a reason Melee did better. Because of a massive amount of content, along with being a massive increase in gameplay speed as well.
Content massively matters, and those NPC roles are what gives the game a ton of life. In fact, how many video games series beyond sometimes puzzle/point-and-click/card games don't have NPC's? That's kind of the point. They're an important parts to games a whole, and increase just how cool a game is. Being playable is not the only important thing. Otherwise, as I pointed out above, Smash would have died off really fast if it had practically nothing of note beyond the super bare minimum. Bare minimum at least has some NPC bosses, after all. Like your general fighting game, and most games with some genre exceptions.