It's a paradox. You stand by the rules Sakurai told (which are absolutely logical and true to the idea behind Smash Bros.)? Ok.
Wreck-It Ralph was released first as an arcade game (TO ADVERTISE THE MOVIE) and he's eligible, even though he is FIRST a character from a Disney movie. It's like saying that other Disney characters are actually toys and not movie characters because they appeared first in Happy Meals at McDonalds. And trust me, IT IS THE SAME THING.
But let's go deeper. If you accept that, then let's take Lucario, which is CLEARLY a videogame character which happened to appear first in an anime (with the intent to, guess what, ADVERTISE THE GAMES). Then what? He's not eligible?
You get what I'm saying?