The paths on the mages look good, I'd just add a couple things about their abilities to make them more "unique":
-give the Gold mages a forge bonus(perhaps even place them in Construction school?)
-animal awe for Amber mages;
-why no undead leadership on the Amethyst mages? As far as I recall, they are skilled necromancers.
Also, I agree that steam tanks should be mid-game construction summons: probably a high protection trampler unable to be routed?
Don't remove them please, because I'd really like to see the gorgeous sprite you'll do for them
