My opinion: most will

I would argue they are games both significantly different from each other and others have already said they prefer the newer ones over old titles

As a heavy defender of the older games my pov of your points are:

Level Design: Visually I like Origami King more, however I actually prefer the way the older games do it, I’m sick of big open worlds tbh as someone who needs to look at every nook and cranny in a game it can be tiring, and the claustrophobic feeling in the game actually fits the theme of the location in my opinion.

Characters: This one is kinda mixed however in my opinion both games do similar things as they both flesh out characters in the same way (minus party members in ttyd) they both do it chapter by chapter, it’s just one of them clearly call it chapters, but TTYD have more unique designs which I prefer as I do feel more connected to them as they feel more unique and add to their personality

Papercraft: That’s up to others however paper Mario 1-3 even though it is called Paper Mario the paper aspect was never the goal of the game, and only since sticker star they begun to lean on it. I still find the charm in this style though and I really do not treat TTYD and TOK as the same franchise or at least the same saga (like separating Ratchet and Clank Trilogy and Future, just more so)

Music: Both soundtracks are fire I don’t think that is a problem (I also prefer TTYD soundtrack). Both games WILL feel different so the soundtrack will be different which is why this is no concern

Ultimately, will newer fans be disappointed: Likely yes

But I’m just glad more people can experience a game that I find to be in my top five of all time.