But still, all of the other characters were primarily geared towards the older audience, with Byleth coming from a rather mature series by Nintendo standards and Hero, Banjo & Kazooie, and Terry all being nostalgic favorites.
And my evidence of FP2 being more child friendly, here it is:
Super Smash Bros. Ultimate Fighters Pass Este pase incluye el siguiente contenido descargable: ● Bonificación de traje de combatiente Mii (Rex)Una bonificación especial para quienes tengan el pase de combatientes. - Peluca de Rex - Traje de Rex ● Paquet
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Super Smash Bros.™ Ultimate: Fighters Pass Vol. 2 ¡Expande tu elenco de combatientes con el pase de combatientes VOL. 2 de Super Smash Bros. TM Ultimate! ¡Expande tu elenco de combatientes con el pase de combatientes VOL. 2 de Super Smash Bros.™ Ultimat
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FP1 was given a 12 rating in Brazil while FP2 only got a 10.
.....and?
Ryu Hayabusa's design has nothing that screams "M Rated", he's just you basic Ninja in design. If anything i would argue Ryza is the on more likely to get censored because we can't have girls showing leg like that you know? (im partially joking on this of course) NJ is gory? Just.....don't have him drop blood. Problem Solved. I mean i played the NES games and i don't remember anything particulary edgy or mature.
Honestly all of the arguments you are giving are basically that Ryu's reveal would have it be "Smash Bros X Ryu Hayabusa", but that's not gonna magically exclude Ryu when he was likely beign developed (assuming he is in Smash) long before ESRB started having a fit (because this whole logo censoring stuff started appearing at the end FP1, before that they had no issue showing game logos).
Saying Ryu can't get in because of M-Rated games is like saying Simon couldn't get in because of Castlevania's later M Rated games. You will be surprised to see how dark the series could get, and i don't think i need to talk about the Netflix show, where Dracula makes a MASSACRE in the FIRST Episode.
Even though said series invented the concept of alchemy in RPGs, which has been used in many games since.
.....that's oddly specific, and not a great reason to add her.
Introducing Alchemy in games isn't what i call "prime candidate for representation in Smash", Hell Alchemy is very obscure in most pop culture and is not a real reason to give her priority over the rest of the 3rd parties at our disposal.
You know what IS extremely prominent in Gaming? Ninjas, and Ryu is among the most popular and recognizable of them. Im not saying that just because he's a Ninja he is more likely, but since Sakurai has clearly a thing for Ninjas (Considered Ninjara, the Ninja Ability in Super Star, he added Shiek and Greninja) i wouldn't be surprised if he finds some appeal in him.
and an RPG? Please, we have tons of them, we surely can have more no doubt but again, other candidates are more well known, requested, popular, prominent and don't have to worry about competing with Ryu Hayabusa.
"MUH ALCHEMY" is unique i will give it that, but aside of that i don't see anyting that makes her a prime candidate. Hell i believe Kasumi is more likely than her, Mai Shiranui Syndrome Notwithstanding.