Felyne is a different case compared to Slime, I think. Slime is THE standard enemy for Dragon Quest. You never play as him as a main character in the core games. Felyne is a character that is customizable and is part of the Hunter's party. He is the partner for every hunter. I understand your point, I think Hunter would make more sense, but Felyne is the most stable character in the series, in the sense of visual identity. And yeah, 4 Capcom characters compared to 1 from Namco is sad, but I don't think there's a written rule stopping any character from joining in, outside of the guidelines that Nintendo follows to choose the characters themselves.
I actually found it funny how this came up. The timing is ridiculous. Right after Deltarune is announced first for the Switch. I also think it would be absolutely amazing to have it in Smash. Out of all the indies, I think Undertale would make the most sense.
Awww... No Cuphead?
But I also have kinda the same feeling towards Minecraft. However, we had numerous stages featuring music from a series that the character in question isn't a part of.
I don't think I need to explain how I feel about Sephiroth.
The idea of having 6 music tracks is surprising, but possible, given how S-E is more open to Nintendo in recent years, Uematsu is a good friend of Sakurai's, and I wouldn't be surprised if S-E had more FF content with Sephiroth and decided to include as DLC so they got more revenue out of it. It would pay the higher royalties demanded, given DLC revenue is shared directly with the third party company involved. And the DQ composer was never against putting orchestral music in DQXI. It was S-E not wanting to pay royalties to NHK bc they usually demand a larger than average amount. I think Nintendo helped them out on that.
And I agree. I feel like this leak is way more believable than the Digimon one.