I'm sorry but I disagree.
I hate to do this type of posts with a mod, but there are too many things I disagree with, and even some factually false statements (such as slippy not being in every game and peppy being removed completely, or the Fox and James thing).
Star Fox has a rotating cast, but the main 4 have been consistent for the most time (including Slippy who never missed a game too).
The only special case is Peppy being "replaced" by Krystal in Assault; that game is set later in the storyline and Peppy is still an important character. Peppy retired from the Star Fox squadron but became a general, and he gets an important role in the story despite not being playable (in Star Fox Command on DS he comes back as playable if I remember well, but that game has loads of characters and not just a main team).
I don't think James Mc Cloud has ever replaced Fox, it was an easter egg/bonus in some games, an endgame unlockable; neither the other way, as far as I know Fox has always been the main character and James was just his father, who has a role in the backstory of the series.
Not being playable does not affect the chance of a character, because there are characters such as Sheik and Rosalina who originally were not playable but still were added to Smash (Rosalina was playable in Mario Kart and maybe other spin-offs but it doesn't count, because look at Waluigi).
Not to mention that the Starfox team is usually not playable as well outside of multiplayer, they are usually controlled by a CPU in most of the games, and they mostly interact with dialogues.
The only thing I agree on is that the champions don't get much screen time, but they are still the most important characters of the game after Link and Zelda. But if you look at it in this way, even Zelda does not appear that much, since the game is mostly about Link going around the world alone.
The game as very little story, but that small story is about Link, Zelda and the champions. Their 4 "side quests" are the only 4 dungeons in the game. You can skip them and go to the final boss directly, but they are still part of the main story. Saying that they only exist to make a boss easier is like saying that most of the Koopalings are unimportant because you can skip most of their fights using secret passages/magic flute/Star Road.
IMO the only difference between Star Fox and the champions is that the champions only appeared in 1 game, so saying that they are not a rotating cast can't be verifyed because we don't have many entries in the series to compare, unlike Starfox. On the other hand, the champions did change in BOTW, since there are the champions from the past and the new champions from the present, and they are different people (just like the old Star Fox team of James Mc Cloud, where the only returning member is Peppy).
I think that the comparison between the champions and the Starfox team is totally fitting as long as we look at Zelda BOTW as a single game, separated from the rest of the Zelda series; it's obvious that if we look at the series as a whole, the champions are unimportant because they only appear in one game.
Honestly, I don't think the champions should be in Smash, since they are intended to be one offs like Ghirahim and others; but I think they are kinda likely only because it's Nintendo who is selecting the characters this time, and because of the huge success of BOTW.
I personally don't even care.
No, the difference between the Champions and the Star Fox crew is the Star Fox crew isn't as consistent or promoted as one group that never changes. Besides the fact they do change the Star Fox crew more than once, meaning they were never meant to be promoted as equals(something they absolutely don't do either).
The Champions are always treated as equals. This has never been the case for the Star Fox crew. Fox didn't even exist till a later game. The crew is "mostly" consistent, but the fact of the matter is that it isn't. It does get changed per the story. But they also aren't hard equals in presentation. Fox was always the main character from the get go. Falco, Peppy, Slippy, Wolf, Krystal, and many others are secondary characters. You can also put James in the same importance as Fox. Daruk, Mipha, Urbosa, and Revali are hard equals by design.
The comparison just doesn't work. Until they start actually promoting one Champion as more important than the other(which has never happened), they will always be on equal settings. The only thing for Sakurai to even look at beyond "what moveset might work better" is who is more popular. That has nothing to do with actual importance regardless.
And yes, they have rotated the cast in small bits for Star Fox. It's not like in Fire Emblem, of course. It's more comparable to how Pokemon is in Smash. Pikachu, Jigglypuff were always the mainstays. The rest varied due to situations. Lucario and Charizard are the hard mainstays after that(whether or not Pokemon Trainer is included). Mewtwo isn't even this, despite its immense popularity. It's been low priority, with Jigglypuff being higher(due to it being super easy to make, of course). Greninja may or may not be a mainstay, but we have no way to tell until the next game comes around.
Star Fox doesn't have a very consistent cast among all games. It has a lot of changes. It just has certain archtypes that are kept. James/Fox(and Fox's son, though I forgot his name) are always there. You're often going to find someone akin to Wolf if not Wolf himself. You'll often have 3 other teammates. Usually Falco is there, respectively. Doesn't change the fact the cast isn't as consistent as people are painting it as. No, it's definitely not. They're rotated it out with "similar" characters to move the story on. Which didn't work well(as Command was fairly bad), but it still existed. It's more of an archtypal cast than specific characters, really.
The Zelda series has a highly rotating secondary cast. Link is the only indefinite constant. Assuming it's not a spin-off or a game Nintendo didn't make. Like the Tingle games or CD-i games. Ganon isn't in every game. Zelda isn't in every game. It's more archtypal designs(just like Star Fox, who doesn't even have a "only this hero is your main guy for sure", due to switching him out for another sometimes). And that's how Star Fox is meant to be designed, having some similarities to how Zelda's core cast is, just with a few more constants(then again, the usual monsters are more constant in comparison than the main/secondary characters in Zelda).
The reality is, the Champions are not really comparable to Star Fox or Pokemon. They're different story purposes. They're just notable members of consistent races that throw them on equal footing to promote. That's their role in the story, to be 100% equal. If they were meant to have someone more notable, they'd have heavily changed how the story works and how they're promoted. The only real difference besides races is as I said earlier, their popularity.
Plus, are you seriously telling me that Falco is somehow the main character of Star Fox or was always meant to be equal to Fox/James? When instead he's his wingman and a secondary(but important) character? There's no denying that Peppy, Slippy, and Falco are important. But they are not nor ever will on equal footing with Fox. And never were meant to be. They're just your secondary major characters. They are not the main character. There's a reason the story revolves more around Fox's exploits(never mind Andross being the main villain in most games, with changes depending the story). They just plain aren't on equal footing. Plus, BOTW doesn't have multiplayer, nor are the Champions playable. They revolve around Link being the main character and each give him an ability along with helping him through a Dungeon. They all do the same overall thing. They're just better written than some characters(though to be frank, they aren't exactly the epitome of writing either. They're kind of shallow. And I don't mean Revali. They're awesome characters, that said).
