In my opinion the following characters are not befitting of the Smash Bros. roster.
ROB - Originally not a video game character, he was a piece of hardware no different from a controller or headset. The two games he was made for didn't even feature him as a character within the game. Since then, yes, he has appeared as a guest character in other games. That doesn't necessarily make him a video game character, as he's never appeared in a title of his own, and originated as hardware. For these reasons he breaks that threshold of video game characters only, he sets a precedent for the game that can jeopardize the future integrity of the roster.
Mii Fighters - The Mii Fighters are creative and fun, i'll give them that. As far as original play style is concerned they're pretty unoriginal and just take on predictable archetypes. Furthermore they can't even be used for online play, due to their gimmick being customizable. Essentially their one perk about being fully customizable is also their Achilles heel. On top of that I feel like their development time could have been put to better use on (for lack of a better word) real game characters.
Wii Fit Trainer - This character was only put in as an attempt to be clever and unforeseen. Which by contrast makes it the exact opposite. Any director could pick any obscure title or unlikely character and make it a "Oh didn't see that happening character". Sure Wii Fit sold well, but at it's core is it really a true video game? Also did any one really want this character before it was shown? No. Another character that doesn't bring a real diverse move set, that's actually really bland. Once again the dev time could have been better spent else where if not on another character than on something else.
Besides those three characters the rest are all personal preference. Sure there's a few odd balls, and move sets could have been improved upon this time around, to enhance the character, but they contribute one way or another to a diverse roster. Yes their is character bias, and yes some people hate clones, but at least it's not a disservice to the game.
I applaud Sakurai's efforts on the following character's move sets. I may not like these characters personally but I recognize what they bring to the game.
Little Mac
Rosalina
Robin
Shulk
Clown Car
and to an extent Villager and maybe Greninja