I like him a lot. Legion doesn't have to always be green fire, even in Antorus raid we had "normal" fire demons.
Geoset choice is very cool, all of them fit the theme of the hero so do the re-textures.
Even a custom spell anim with whip is a nice touch (not for the recipients of the whip ofc).
The only thing that's lacking in quality compared to the model is the icon. I would try to make a model without all the fire FX, face him to the side (for more dramatic lighting), and use that as a base for icon. Small highlights of the edges of the armour might help out distinguish his frame in the icon as well.