Lets compare Khorvash to another troop with a similar mana cost and effect. Moloch, for 14 mana, deals Magic+3 true damage and drains mana, boosting damage dealt by mana drained at a 2:1 ratio. Not only does Khorvash do this twice, at the same ratio, he has four more base magic plus three magic from the Leader trait. That means, in order for Moloch to deal as much damage as Khorvash, he has to drain a total of 14 mana from a troop. Khorvash deals full damage all the time.
Did I mention that he does this twice?
Khorvash is not only a double Moloch with more damage most of the time, he also stuns both enemies. If he were to have a cost proportional to his ability on scale with Moloch, he would cost twenty eight mana plus however much you determine that two stuns are worth. That is what we call mana efficiency.
Next, lets look at the mana cost itself. 14. Okay, what does that mean? It means that with +1 to each of his colors on a banner, if you get two surges (3 + 3 from surge + 1 from banner) in a row (~25% chance. Probably higher for most people), he’s full. So, without any 4-5 gem matches made, or other troops creating gems to fill his mana, he only needs two matches to go off. Two gem matches for 3 (base damage) + 9 (base magic at max level) + 3 (Leadership) + 4 (Magic kingdoms at 10) + 2 (Guild) = 21 damage, 25 if you have your kingdoms at five stars, twice, the double mana drain, and the double stun. For the hell of it, lets put him in a team with a troop that has Blessed (Mercy). 27 damage. Double Moloch plus double stun for two gem matches.
This is without factoring in the tankiness granted by Stoneskin plus his extremely respectable stats (45 base effective HP(life+armor) compared to Gorgotha’s 49. 51 if you include Leadership) and his third trait, which stuns on 4-5 gem matches. His body is respectable, his traits are very good at WORST, and his ability is worth well over double what another troop does for the same cost. Broken? Matter of opinion. Well above the power curve of the game? Definitely.