He has a running animation, it just looks like he doesn't because he swings his arms while running. I don't know why SEGA made it look like that, but I don't really think it's a problem, and if anything makes him unique. But I can understand if you didn't notice at first.
Also, to address your other concerns, X Sonic has the same stats as Sonic (I literally copy-pasted them over), so I think the reason he seems slower is because of either his animation speed or his ability. I'm willing to bet it's his animation speed.
---------- Post added at 09:02 AM ---------- Previous post was at 08:50 AM ----------
as Pyrakid said, why not using those Spin Slash Spindash sprites for the character?
also, was forgetting: the super form for this character is... not good
just a buff and a recolor with Mania Super Song, nothing else new
i mostly wish to remove or change it with something else
There are no Spindash Spin Slash sprites. I don't know where you're getting that from, but it's okay.
Also, reguarding the super form, I wanted to keep this a secret, but if you move fast enough and Spin Slash into a wall, it causes a quake that kills nearby enemies (Think Hyper Knuckles). It's not supposed to be much because of the fact that he has a screen nuke. Other than that, There are no pre-renders for the super form, probably because Sonic Xtreme got canceled before it could get to that point in development.