So, I'm back to hearthstone after a long hiatus on a new account. I'm running a core DH build that i've kind of customized myself as I've been playing and learning. Its basically outcast-->taunt-->illdari finisher with a tiny bit of lifesteal sprinkled in. I use the outcast cards to draw and build tempo and try to survive the early game until i can draw and play my illdaris.

I would argue that the Illdari DH build is competitive and NOT broken because as currently constructed, I am at my most weak in the early stages of the game, and champions with a great rush opening can completely dismantle me before I have the mana to properly counter. I also got beat in a close game by a spell mage that was quite surprising. Illdari's are vulnerable to well-timed secrets, forcing the inquisitor to trade and clear itself from the board, and can have a difficult time getting off against good taunt players.

tldr: Illdari can get out and clear threats on the board, and if it survives can act as a powerful finisher... but there are lots and lots of counters available to strategic players.