Kid Icarus straddles over-representation. Bolstering three characters, six items,
bonus music on the 3DS, an
overwhelming number of baddies in Smash Run, and a heap of
recorded dialogue in a game that otherwise does not have much sustained speech, one might mistake Kid Icarus for one of the thickest pillars of Nintendo alongside Mario, Zelda and Pokémon. I don't even want to look up how many trophies this series has to its name - probably one for each charm on Palutena's sash.
I agree that content should be added on its merit. If a character, setting, or concept has what it takes to make a good Smash Bros. fighter, stage, or item, then by all means, divert the resources toward it and make it happen. With Kid Icarus content, however, it seems like Sakurai was overzealous about his most recent project, and wanted it to be placed on a higher pedestal than it warrants.
If you don't have the 3DS version and haven't played Smash Run, then you have not even experienced the full implications of Kid Icarus baddies by the barrow. Once you've been pursued across the map by a Mimicutie, into the gnashing fangs of an Orne, you can't speak from the heart how infuriating it all is. From the Wanted Clubberskull tanking all your Powers, to the Mahva's barrier gimping an otherwise easy recovery and stopping you from reaching rewards, the KI enemies are altogether the third biggest killer of fun in this mode, after lack of online play or interaction on the map. They're all annoying and you're just surrounded by them in every play-through.
The nepotism going on has left a bad taste in my mouth. I groan whenever I have to play as or against Pit, Palutena or Dark Pit.
I've never felt like that about any character in the history of Smash before. And I promise it has nothing to do with them "taking a slot" from a character I wanted, because I am not that loyal to any particular character anyway. It's just burnout from seeing so much content from games that are either not very good (first two games) or don't appeal to me remotely (Uprising).
Otherwise, the content balance has always seemed about right to me.