Punch-Out is an arcade game that got ported to NES. Calling Punch-Out a Nintendo game is like calling 1943 a Nintendo game.
... You realize that Nintendo made arcade machines, right? That Punch Out have several games, like an SNES game and a Wii game, right? That Miyamoto himself designed the First Little Mac, the wireframe version?
I kinda like FE, but 6 characters is way too much. Marth, Roy, and Robin are fine. Actually, I'd prefer Robin been cut so his gimmick could go to the Robin from Golden Sun, but I've basically given up at this point. Lucina is iffy, but because Marth is so trash in this game I give her a pass for being a somewhat viable character. Ike is a questionable veteran. He was the new Lord (shut up) at the time, so it makes sense for Brawl, but given that Shulk is basically Ike with new specials he seems redundant. Now we have a sixth FE character. Until Awakening, FE has never sold well. No, not even in Japan. Yet we have 6 characters from the series. For comparison, Pokemon has 6 playable reps. There are over 700 Pokemon. Even if we assume that only about 1/7 of them are good fighter choices due to things like difficulty in translating to Smash (like small, large, or floating Pokemon) or being from the same evolutionary line (it wouldn't make sense to have Bulbasaur and Venusaur), that still leaves a ridiculous 100 possible fighters to choose from.
But does Fire Emblem have an "emblem ball"? Serie representation doesn't stop at the CSS. For example, many people says "but Zelda didn't got anything!". These seems to forget that the series got 3 new assist trophies, and they are meaningful characters, many items, and many stages too, 7 stages on 3DS and WiiU, compared to 3 stages accross all Smash games for FE. Sure, Zelda still have many past stages, but we can't forget Temple, right?
On Zelda's case, there's also the matter of protagonists: all that is important is already there: Link, Zelda and Ganondorf are all that we need, and everything is minor, compared to them.
Both Zelda, Fire Emblem and Pokemon are 3 different cases: the first one revolves around 3 characters. Fire Emblem have different main protagonists in almost each games. Finally, Pokemon is actually lacking it's protagonist: the trainer. And the pokémons, while some of them are popular, are "only monsters". Some of them have specials things to them (Charizard's mega evolutions, Mewtwo is a legendary, Lucario often have a special role in the games), yet, they aren't the heroes of the main games.
That's why FE have a more "extensible" cast of potential smash fighters to me: whatever happens, as long as there's Fire Emblem games, there will be protagonists.
Also, and this is a personal point of view, but "I don't count Lucina and Roy", and therefore, there's "only 4 FE characters". At least, 4 pure original movesets. Ok, it's obvious because Lucina is a bonus, intended to be a costume at first (and we usually don't count the Koopalings or Alph when it comes to serie representation). Roy, it's only my own interpretation, but he came back because of his Melee's popularity. Like Lucas, his initial cut means a lot to me.
Those two cases are different from, let's say, Ganondorf and Toon Link. Both are semi-clones, who stay that way to not alienate the fans of their movesets (and I personally enjoy a lot Captain Ganon), both both came back in the base game, and weren't meant as a costume.
... And wait, did you really compared Ike and Shulk and said they are redundant?
Then there's the issue of who has to be cut. A lot of people don't want to admit this, but there is such a thing as "slots" and a character can, in fact, waste one. There is only so much dev time available, so time spent making one character is time spent not making a different character. Kamui clearly has a lot of unique traits to him, I don't think anybody is denying this. This means that a lot of dev time was put into making him instead of a different character. In fact, he looks like one of the more time-intensive new characters, based on his animations and his new sticking mechanic. Now go watch the Smash Direct again and tell me if it's missing anything. Like... Bayonetta's aerials? Look again, all I saw was her fair and something that looks like her nair. I would guess that if you had cut Kamui and maybe one of the less time-intensive other characters (like Lucas or Roy, as much as I love Our Boy) we would have gotten 2 new, unique characters for the same dev time.
Every moves are shown during Bayonetta's trailer, except for some throws.
http://smashboards.com/threads/bayonettas-moves-gifs.426077/
And I doubt that cutting Corrin in favor of other character would have granted more characters. And if it means getting less interesting and unique characters, I definitely pass.
Also, "wasting a slot" is almost always a matter of personal taste.