but dixie wouldn't have been a clone
How do you know that? Diddy doesn't really have any trademark moves other than his cartwheel, which is just one move and can be replaced with Dixie's hairswing.
And Wolf isn't a clone, fuck you.
It's interesting to note the order of the
instance slots for the unused characters (the "forbidden seven") that are linked to on that page:
-all of the characters present in Brawl save for Jigglypuff, Toon Link, Wolf, Snake, and Sonic are listed in a single unbroken list.
-Pramai (Plusle & Minun?) is listed right before Jigglypuff, right after R.O.B., the last of the unbroken list of present characters.
-Mewtwo, Roy, and Dr. Mario (in that order) come right after Jigglypuff.
-Toon Link is listed next, followed immediately by Toon Zelda and "Toon Sheik."
-Wolf is finally listed after Toon Sheik, Dixie is listed immediately after him.
-And then Snake and Sonic are listed last (of the proper playable characters--Giga Bowser, Wario Man, the alloys, and a debug Mario are listed afterwards).
Regarding Jigglypuff, Wolf and Toon Link, what also is worth noting is that up until ROB, every character actually plays a role in the SSE story, while those 3 are bonus characters you'll have to unlock after beating the entire story mode.
Sonic is the very last character that was added in the game (but was important enough to get an actual short cutscene in SSE and be part of the story), and I assume that Snake has been put in that later spot there because he was 3rd party.
I assume that they intended to stop adding characters after ROB, but then thought of bringing back some of the older characters to beef up the roster, however, scrapped most of that during development.
Pramai might've been a sort of alteration for Pichu (if Plusle & Minun is correct), and they included Jiggs, Mewtwo, Roy, Doc and Young Link as Toon Link. They also thought of giving Zelda a young version (including an according Sheik), but that, among with all the characters other than Jiggs and Tink had been scrapped. Dr. Mario, Pramai and Toon Zelda/Sheik had been scrapped before Roy and Mewtwo, though, because of the victory themes you mention.
Since Mewtwo also has a placeholder sound for the Wiimote, which Roy doesn't, I actually would argue that Mewtwo was cut in the very last second due to some issue (maybe problems with Game-Freak? Or they had problems implementing something he did?), so they had to put in another character. They didn't want to add any of the already scrapped character concepts, so they whipped up drafts for Wolf and Dixie, and Sakurai might've just liked Wolf more than Dixie, so they stuck with Wolf.
Also worth noting that the Pikmin are not listed separate from Olimar (all under one instance called "Pikmin") but Popo and Nana are listed separate as is the Pokemon Trainer from the individual Pokemon.
Olimar uses the Pikmin as part of his moveset, they are not separate characters, while Nana uses a different moveset from Popo (her moves have very slightly different properties in some cases). They also have different soundfiles (since they have different voices). This is the case for Pokemon Trainer as well - PT is basically a randomly selected Pokemon, while the 3 actual Pokemon are, well, the actually selected Pokemon.