There's an upcoming patch for Super Smash Bros. on 3DS that will tweak balancing in the game, yet while some will call for that change to weaken Little Mac, statistics suggest that such changes may not be necessary.
This writer's been on the end of some sound thrashings by Little Mac players in the online For Glory mode — with a gauge that can deliver instant KOs and powerful combinations he can be a beast to fight when in the hands of a skilled player. He's also what should be considered a specialist character, however, as his default side special can be awkward to execute and — in particular — he's an appalling jumper. The odds of recovery when smashed off the stage are rather slim with the underdog boxer.
A combination of these factors seems to have contributed to Little Mac being — statistically — the worst character in the game. Nobody loses more than the plucky fighter, with Sakurai-san explaining the reasoning in detail.
For Super Smash Bros. Brawl, the individual character win ratios lined up nicely in a staircase format, but [for Super Smash Bros. for Nintendo 3DS] one fighter has a significantly low ratio. It's Little Mac.
Little Mac is a fighter with very pronounced strengths and weaknesses. While he has an enhanced dodge and megaton-level punch for aggressive play, he has very weak jump power and a simple back throw along with a follow-up attack prove to be crippling.
It appears that the biggest reason for his low win ratio is because people fall under the assumption that 'Little Mac is strong!' and all rush to use him only to get pummeled in return. He gives the impression of being able to win easier than other fighters which leads to more people using him, but in reality, he's a difficult character to actually continuously win with.
To those expecting these patches to ultimately balance characters out to have similar overall stats, however, there's a categorical rejection of the idea from the game's lead designer.
I believe that averaging out character stats is a bad move in both play and competition.
So there you have it, while talented players can certainly clean house with Little Mac, coming across the boxer in an online match doesn't necessarily mean that defeat is inevitable. If anything, you should fancy your chances.