Limiting movement does not make the game any less 3D. A drawing that looks like it has depth is 2D because it doesn't really have depth. Move the drawing around. You can't see behind the things that are in the front, no matter what you do. In Smash Bros., however, if you move the camera (which you can do by pausing the game and using the control stick) you can see in 3D.

As a side note, even if you couldn't manually control the camera, it'd still be 3D because the world and the characters are made of 3D models. A simple hack would be able to move the camera to show 3D space. The characters are confined to an X,Y axis, but that doesn't mean the entire game is. There's no reason there couldn't be something in the game that does wander around in full 3D. In a 2D game, everything is flat, making that impossible.

As for Kishi's example, that does nothing to help your case of Smash Bros. being 3D. In Fez is even less 3D than Smash Bros. xP

If you want to argue some more, I'll reply tomorrow. I refuse to be that guy in the XKCD comic who won't go to bed because someone is WRONG on the internet. xP