I would agree with that if we didn't have the 5 3rd parties we have, all of which are either genre-defining or known worldwide by gamers everywhere.
Think of it this way. People all the time think about certain criteria for Nintendo characters getting added to Smash. Think back to the first Smash. Who should make it? Mario, Luigi, DK, Link, Samus, Pikachu...all super famous or groundbreaking. Or just overall popular. Why should that mentality break when considering 3rd parties?
Not to mention, why should a character like Shantae suddenly be lined up next to
? Or better yet,
? If I were thinking of the Top 3rd parties, Indie characters are not what I think of. The proof comes from what we've tangibly been shown from Sakurai/Nintendo.
Aside from that, Sakurai used the term, "not just anybody". So far, he's kept his word with that statement. None of the 3rd parties added have been a character from a minor 3rd party series. I mean, think about the biggest series' in gaming...
Mario, Pokemon, Zelda, Sonic the Hedgehog, Pac-Man, Mega Man, Final Fantasy, Street Fighter, Metal Gear Solid, Uncharted, Halo, God Of War, Rayman, Call of Duty, Gears of War, Grand Theft Auto, Minecraft, etc... sales be damned. I'm talking more about the hype surrounding each release mind you.
Obviously not every series in that list will get into Smash. I WOULD be fairly upset if a COD soldier got into Smash. I love Shovel Knight. I just played through the game for the first time, and I think he'd be a fun Smash characters. However, I'll fully admit he really doesn't stack up with the other characters right now. Years down the line? Maybe. Right now? I don't know. I think he and other Indie's need to establish themselves and rise from obscurity. A **** ton of people know who Cloud is. There are reaction videos everywhere because of that trailer. I don't think you'd see similar reaction to Shantae or any other Indie.
My point is, that while there may not be any sort of actual statement, I don't think there needs to be an official statement telling us that 3rd parties need to be at the level that we've been shown. There's, quite frankly, no reason to believe otherwise, simply based on the virtue that Shantae, Shovel Knight or any other indie
does not compare to our current 3rd party cast.