To me, the problem with Euden or Dragalia Lost, in general, isn't that adding a character from a game that isn't available in a region would be seen a "disrespectful" or whatever... is that if Nintendo doesn't want to put the effort to localize the game for the European market, why would they suddenly care enough to push the game by adding its main character in Smash?
And yes, maybe that kind of decision doesn't fall entirely on the main branch: maybe NoE didn't want to have the time to localize the game, or maybe they didn't want to get around the "anti-gacha" laws, but... idk if something like Genshin Impact can release here without any problem then those laws are something that can be dealt with.
Also, they don't necessarily have to give it a FIGS localization, they could have just released the game in English like they are doing with the FamiTan remakes.
And I get that someone could argue that they still care enough about the game to some crossover events with Capcom to with P5 Strikers but I think it should be noted that Persona 5 has collaborated with many mobile games and that Capcom is notoriously easy to work (something something Ryu was in that Family Guy flash game).
Like they are nothing to sneeze act but they aren't exactly groundbreaking deals, and we still have to acknowledge that outside of those rare events the game has been less than a blip on the radar.
Ultimately I don't think us getting DL contents in Smash is impossible but I definitely won't be surprised if it doesn't even get a Spirit event.