I'm not sure if I fully agree with your opinion, re-playing the 3DS games are on my backburner, but I can see what you're getting at.Tons of Robin's attack animations, as well as his general movement, rely on him being a sort of clumsy and unrefined swordsman, as shown by things like his dash attack, tilts, back air, and down smash, to name a few. Celica's swordstyle is a more graceful and elegant rapier-like style. Add to that that Celica's almost always a magic user over a sword user (except in Warriors due to time constraints that wouldn't be present in Smash), and that Robin only uses magic in his jabs and specials, and it honestly just isn't representative of Celica in the slightest.
Echoes I think are a confusing mess to pin down a specific vision of compared to regular characters. There has to be a base character to go from but they can have/not have new moves, can have new animations/re-use animations, can play differently but have different fighter classifications.

All I know for sure is that Alph/Rock Pikmin was robbed.