I completely understand the sentiment on how unique fighting game characters can be, but I think people are looking for something a bit more than carrying over a command list and playstyle from their original game. Fighting game characters are probably the easiest to transition into Smash, but are extremely straightforward, and basically you know exactly what to expect from them. I stand by the fact that there are tons of more interesting characters that can be selected, especially characters from completely new genres.
Saying that fighting game characters are easier to translate in Super Smash is untrue. Super Smash plays differently from almost every other fighting game, and making the transition to a platform fighter while staying true to the character is complicated af. We knew exactly what Terry could do and the end result was unpredictable. A backwards side special, dodge attacks, a limit break that doesn't expire, hold buffering tech, and so on. There's a reason that Heihachi was dropped in the last iteration; Sakurai couldn't figure out how to interpret his mobility correctly.
I want more genre as well, but fighting games have sub genre categories that aren't in the roster. 3D, beat em ups, weapon-based, and games classified as anime fighters all come to mind. Seeing any kind of character play by Super Smash's rules is fun and different so Idk what's wrong with wanting fighters. I think we could use more of them.
Except that platform fighters like Smash bros works completely differently from fighting games, so the nuanced character quirks are never going to translate as well as from when you go from a 2D to 3D fighter. In Smash, there's a lot more freedom of movement, and aerial mobility is a huge factor. It's is an environment that fighting game characters simply can't take advantage of because their design was originally made for tight 1v1 gameplay. Compare this to say, platformer characters, who were designed by how they move and jump around in a free environment. I'm not saying that a new fighting game character can't be unique, it's just that other genres can offer a lot more to Smash that wouldn't even be possible in traditional fighters.
The nuanced character quirks are what make them interesting. Air dashing is a mechanic we do not yet have. There are fighting games with mechanics that make characters fly around the screen, fall slower, and so on.
Fighting games are why we have Smash in the first place. My most wanted character is from a visual novel, but I know that Sakurai will turn to fighting games for inspiration to flesh out their move list.