8 mana to deal maybe 12-14 damage if you have some of those 0 cost +2 deal damage cards? it's efficient, but it's not exactly much different from a pyroblast, and it's technically less card efficient than 2 fireballs with about the same return, and he can still get cockblocked by taunts.
Now Varian Wrynn, that's a warrior legendary to get behind. Varian into Grommash is just not fair.