I'm not entirely sure, but I'm under the impression that the hardware differences between the 3DS and GCN/Wii are not black and white. The former can do some things easier, others less so. Based on games on both CPU calculations and pipeline bottlenecks appear to be a weakness within the 3DS compared to console hardware, even dated console hardware, which makes sense given the portable architecture verses larger, power hungry home hardware. Resident Evil is my favourite example. Revelations and Mercenaries are both doing shit with shaders easier than the GCN and Wii ever did (bump map all the things!), but the LOD pop-in on assets and animations is far, far worse, as is (I think) precision of collision detection. Where Resident Evil 4 can pretty comfortably render a lot of opponents on screen with close-to-if-not full animations for each, the 3DS struggles and has to start significantly reducing model complexity and animation frames, despite at the same time lathering said models in bump/normal maps that weren't present on the GCN/Wii.
Smash 3DS would theoretically have similar issues with someone like Ice Climbers, where in a 4 player match your effectively doubling your on screen character count and thus models, animation frames, AI calculations, etc, alongside all the assist trophies, smash balls, and items. The 3DS is no slouch in making those characters look good, but making all those calculations could trip it up.