The skills have different threat multipliers. Overpower uses a x4 multiplier, so threat = damage x 4. Steel Cyclone sadly is on a x1 multiplier, so while the damage is much higher, the resulting threat is lower. Defiance is a 50% threat boost with 25% damage reduce, so the total numbers look something like this:
OP = 120 pot * 0,75 * 4 * 1,5 = 540
SC = 200 pot * 1,5 = 300

* This is assuming that the Threat tables at http://valk.dancing-mad.com/tables/enmity-tables/ are accurate