There is absolutely nothing wrong with telling people their favorite character suggestions are bad. Insofar as character speculation has a purpose at all, and it's a valid position it has no purpose and shouldn't be done at all (I'd support; we could talk about how Smash actually plays instead!), why would you even want to discuss it if your viewpoint isn't open for discussion and criticism? Discussions in which everyone agrees are boring, and any venue in which it's not possible for someone to disagree with you is a venue in which you can find no real satisfaction from people agreeing with you either since you know it's an artificial echo chamber and not a real perspective.
I'll actually give the following hot take that is probably the most controversial of them all: it doesn't actually matter at all who gets in. It would be somewhat damaging if they cheapened the game with anime characters or just picked really boring characters like Bandana Dee, but the game would still be fine and most actually likely choices would improve the game probably by about similar amounts. In the end, they're going to build so many quality, interesting movesets, and what is actually going to make the game fun to play will be the interaction of those gameplay elements and not the pretty pictures that represent them. I think we're all gamers and all have games we like so it's not insane to care somewhat, but if you actually care enough to get like emotionally hurt or whatever over this, you need to rethink your hobbies because even as a ridiculously huge Smash fan I can say it seriously does not matter in the end which characters are in. I'm not just trying to be mean either; we're only a few months away, and we know there aren't a lot of characters left so if your favorite isn't already in sorry their chances aren't great literally no matter who your favorite is so you might as well be ready for it now.
To address another topic, the case of Dracula's appearance is interesting because it's true he's definitely overall a non-video game character. He's not playable and more of a cameo so it's even less interesting than usual to dive into, but there are a few factors. For one, the novel Dracula is actually in public domain so there is no licensing at all for him from that perspective; I think for characters more than 100 years old before copyright law was rewritten to be eternal it's a looser thing. On the other hand, the Dracula from Castlevania is definitely a pretty specific take on the classic character; it's kinda like most elements of the Kid Icarus games clearly borrow from Greek mythology but change it up pretty heavily (see: Medusa). Dracula is a little bit stronger of a tie since Castlevania more expands on the novel than reimagines it (the novel Dracula is actually considered canon to the Castlevania series), but it's not completely outside of reason especially for just a boss character.