Fine, I apologise for my wording... Moving on...
The more time moves on, the less I see Kingdom Hearts as viable competition. One angle that's often not look at is how characters are depicted in Smash and how they come into Smash. Most of the third parties we get are strong enough to represent the entire company they come from. Sonic, Snake, Pac-Man, Megaman, etc. This makes sense because they are the stars of multiple games and the main characters of their respective franchises. Then you get to characters like Cloud and Joker who only star in one mainline game.
Cloud- Pretty much the face of Final Fantasy and Square Enix. No arguments there. It doesn't matter that FF VII wasn't originally on Nintendo platforms, Final Fantasy and Square Enix already have a super rich history with Nintendo. Tons of games. Tons of exclusives. Their relationship is technically over 30 years old. Cloud is pretty much the signature character to represent Square Enix as a whole.
Joker- A similar situation to Cloud but much more new. In a very short amount of time, Joker has pretty much become the main mascot of Atlus. Coincidentally, Altus has had a relationship with Nintendo about as long as Square Enix:
https://en.m.wikipedia.org/wiki/List_of_Atlus_games
Persona has very quickly become Atlus's signature series so, again, it's irrelevant that Persona 5 wasn't originally on Nintendo platforms. Atlus has been a pretty solid Nintendo ally for a long time so it's another case of "who better to represent them than their main character?" Like how Cloud is basically the signature Square Enix mascot, Joker is more or less the same for Altus.
This is where we move onto Sora and Kingdom Hearts. Kingdom Hearts is an overwhelmingly Sony favored series. All the mainline games have been on Sony platforms and there's been zero ports. Kingdom Hearts had a spin-offs on Nintendo handhelds but all eventually stopped being exclusives and were completely remastered on Sony platforms... Multiple times. On that end, Kingdom Hearts isn't exactly a super Nintendo friendly series. It's overwhelmingly Sony.
Let's compare this to something like, say, Metal Gear Solid. Metal Gear started on the NES, Metal Gear Solid started on the PS1. The first remasters for Metal Gear Solid were on the GameCube. Metal Gear Solid also got several ports to Nintendo platforms too. It's a reverse situation to Kingdom Hearts. Kingdom Hearts had Nintendo exclusive spin-offs but then got significantly better remasters on Sony platforms. Metal Gear Solid had Sony exclusive mainline games but then got remasters on Nintendo platforms. That's where the difference lies.
So, as kind of a recap, Kingdom Hearts is basically a Sony franchise. Born on PlayStation 2, gives the mainline games and remasters to Sony, the Nintendo exclusives were super short lived, etc. It overwhelmingly gravitates back to Sony time and time again, it doesn't exactly help that there's no ports yet despite being possible as early as the Wii U/3DS, and the last one released on a Nintendo platform was 2012 (and then fairly quickly lost its exclusive status). Yes, Smash has turned into a celebration of gaming but Nintendo is still the frame of reference that everything gravitates towards. Series are not primarily celebrated exclusively for themselves but because of their overall relationship to Nintendo. This is why "Sony" characters like Snake, Cloud, and Joker really aren't because, in the big picture, Nintendo is still a big part of their companies and/or franchises. With that in mind, Kingdom Hearts is not important to Nintendo and Nintendo is not important to Kingdom Hearts.