Whenever you talk about balancing, you have to remember that their preferred metagame is 4-for-all with default settings.
And yes, the cast is very balanced in this setting.
Sonic and Falco make up for difficulty getting a point by ease of getting a Smash Ball and using their ridic Final Smash.
Meta Knight has limited crowd control options and a poor defense against thrown items, as well as a terrible final smash, but he's absolutely amazing if he can single out an opponent.
Ganondorf and Falcon steal kills like nobody's business.
Samus has an immensely power Final Smash that turns her into a character that can handle her own a little better, but is fragile and weak to having items used against her.
Zelda's Din's Fire can snipe the Smash Ball from anywhere, and then she can transform into Sheik to use the low-angle Light Arrow. Sheik is fast and can get to items really well, and the chain will bat away any weak item attacks, while Zelda will use stage control from Assist Trophies and co to drag people into her smashes.
Olimar, as we all know, has a great basic game, but once he's offstage, an assault from items will be a lost stock if you can outwit the whistle. As well, his final smash is subpar.
Ice Climbers are extremely polar. They have great smashes for clearing an area, interesting behavior with items, but in general will die painfully in a crowd, especially having the worst final smash. The thing is that they can potentially remove any and every single-target threat through a chaingrab.
We can argue D3 can do the same with his chaingrab, except it's much harder to land with items flying everywhere, while Nana can just Blizzard wall her way past some onslaughts to get Popo into grab range.
Anybody else want to comment on the 4-for-all All Items on Low metagame?