So you haven't actually seen the impressions of people who play RFA. Because the people who played the game and support its character are not the same people who say they would play exactly like Wii Fit Trainer.
Not to mention that's an opinion so superficial it would die the moment the character were to be revealed, because the characters are just that different.
So, you would have Dragaux doing generic kicks and punches? Because that's all the baddies do really, except for the ones with unique body shapes - like the mat - that Dragaux couldn't imitate. Or did you mean randomly summoning mooks? I don't think either of those are very unique, especially when compared to RFA's mechanics of summoning multiple giant glowing fists, abs and feet to attack.
And, uh, agree to disagree on a big dragon being more interesting. We already have several big dragons in the Smash roster, not to mention it's a very common trope. How many fighting games, or games in general, star a trainer with a pilates ring? That stands out more, it's wackier and more inventive.