Sakurai has multiple articals that you can find translated by source gaming where he talks about how Japanese games don’t sell in the west anymore. He was recently given an award for smash because it was able to sell world wide. The “too Japanese” thing is legitimate because it’s a concern that he has had in every smash. And if you want confirmation of this just look at the state of smash now. While every character in the roster is of Japanese creation except for Diddy Kong it doesn’t feel Japanese. That’s an intentional part of sakurai’s design because he has been trying to no alienate the west.
Marth is preeeeety Japanese. I know his games technically take place in fantasy Europe his game series was Japanese only when he got added to Smash, he's stuck speaking Japanese forever in Smash localizations and he looks exactly like a standard Japanese character from an 80s anime.
Greninja is a ninja. His final smash involves flipping a tatami mat and then silhouettes against a large moon that's like peak Japanese. And if Sakurai really wanted to avoid specific cultural references that'd be the easiest place to avoid them because there's an extreme excess of viable Pokémon candidates. I guess you could argue Ninja are well known around the world but so are Samurai like Takumaru. Lukario while not Japanese also has very non-western influences.
If you mean characters don't seem like they're from a Japanese game as opposed to direct references to Japanese culture (because "too Japanese" is hella vauge) all the KI characters are veeeery obviously anime inspired, as is the entire game of KI uprising, which Sakurai made. And of course all the FE characters.
Also not sure if you're counting 3rd parties but Cloud is a J-Rockstar with a sword and Ryu is literally a representative of Japan from a game about fighters representing different countries and his stage is a traditional Japanese dojo.
More importantly though, what very Japanese Nintendo characters or even aspects of characters that you'd expect to be in Smash have been omitted? Like....Samurai Goro? Hanafuda? Piston Honda? Like none of those are characters I'd expect even if the dev team were completely neutral on cultural representation. Smash is a Nintendo crossover and most Nintendo games aren't obviously Japanese if you don't know the company, so that's just going to happen.
You're right that Sakurai is seriously concerned about things having global appeal and the fact that Takumaru isn't well known outside of Japan is a huge hurdle for him, in addition to the fact that
he's not even that big a deal in Japan, unless Sakurai picks him to give exposure to him. But I don't think that the character itself feeling Japanese has much to do with it or would matter if they were a very Japanese character who is popular in the west like Ryu, and pointing to the current roster doesn't seem to indicate much of anything either way from what I can tell.