Advantages of Mages over other races.

Yes, the developers did a great job adding obsidian golems; they are useful creatures. I tried them out for the first time in the first mission of the last campaign, Tribes of the East. I was impressed. I didn't immediately notice their ability, but when I replayed it, I started leveling up Zehir's Chaos Magic. Obsidian gargoyles also helped as an obstacle for Death Knights and Crystal Dragons.
Many people criticize them, but I think they are useful creatures for mages because of their immunity to water/air/fire and their decent defense for a second-tier unit. They are more of a support unit than a combat unit, which is probably not what people expect.