I don't understand how Falco isn't notable. He's been with the series since the beginning as part of Team Star Fox and had a notable role in Adventures, Assault, and Command. He's basically Fox's best friend. There's also the matter that he's been with Smash six years longer and was seen as significant enough to not only not be cut in Brawl but retooled too. On the topic of semiclones, I honestly don't think custom moves will hurt anyones' chances anyways because we still have Toon Link who shared the most similarities with their counterpart of any semiclone in Brawl.
He's just another random ally and didn't bring anything of note to the overall series in the end. He has a nice personality(so to speak), but that's it. He didn't give notable advice(Peppy), play a major role in the story(Krystal when she appears), adds gameplay choices via vehicles(Slippy), or is an actual villain/anti-hero(Wolf). He's just there among the "main cast" and that's it. I don't see any true notability among the series whatsoever. He's just pretty much the Toad at this point.
StarFox just had enough appeal to get 3 characters. Falco's only reason for addition was because he was a clone, not having the potential to be highly unique from the start. Wolf was still on there while being unique from the start. He didn't remove any clones that were distinct to a degree anyway(except Roy). Falco is a different person from Fox. Ganondorf, Young Link(updated to Toon Link) were completely different people and had potential for interesting movesets. Dr. Mario was still another version of Mario and a fairly easy choice to cut, while Pichu was not terribly different from Pikachu except hurting itself. Mewtwo was worked on, but had to go against 4 new characters and 2 of the original 12. Not exactly easy to deal with(he also was irrelevant anyway, having zero movies, anime, or game importance anymore. Not that he was important game-wise either. He was just there like the rest of the Gen 1 Legendaries).
There's only one worth cutting if any, and it's still Falco. Wolf also fills out the more needed villain slot as well. It'd be as ridiculous as getting rid of Bowser or Ganondorf at this point. And no, I do not consider being in multiple games
alone to matter. Falco wasn't there from the start, he was just a quick clone addition like the rest. His real importance in the StarFox series is "just there for the ride". Even Jigglypuff has the original 12 status. I can't see Sakurai looking towards StarFox or Mother for cuts anyway. Pokemon, Fire Emblem, and 3rd Party are really the only ones that make a bit of sense overall. He's done it before. Mario too, but he already returned all of the Brawl guys, and Dr. Mario has no reason to come back at this point(and custom movesets should allow you to remake his Melee moveset, making a costume fine now. The reason it wasn't a costume was because of the differences between the two, namely the Megavitamins, something regular Mario just can't do, till possibly 4 anyway). One thing to also keep in mind is that Pichu itself starred as basically a protagonist of a movie(as the Pichu Bros.), Ganondorf is another main villain, Roy is a main character, Dr. Mario is a main character(of his own series), and Young Link is also the star of his own set of games, especially according to Sakurai. Falco is not a main protagonist, stars in anything besides a secondary player, or is a main villain. His importance is
vastly overstated. Also doesn't have the original 12 status, another kicker. I don't see him staying between him and Wolf at all. He literally has
nothing over Wolf at this point.