I don't think Unchained > Steel Cyclone for generating AOE threat. It's a single-target opener, that's it.

Overpower I guess technically goes from 90 to 120 potency under Unchained, conal and 130TP. So, 30 Potency AOE is gained, you need to drop 7 Overpowers to match Steel Cyclone which is 200, circular AOE and TP-less and doesn't take 7 GCDs to apply its effect. Burst Enmity >> Sustained Enmity for AOE, then you can focus on putting the damage debuff on as many mobs as possible.