I don't know why you're still throwing around the numbers. Like I said before, at best onslaught's 100 damage is only there to make up for the loss of IB. SP combo is ~200 potency + 10 BG gain per GCD, but requires a full 7.5s combo to hit.
Removing the 100 potency and making it cost 0 would really be all that's needed to make it a worthwhile ability - the 20 cost makes it too awkward to use as is for it's current purpose, and the walking time it saves varies from none to 2 seconds at best. It won't always be 200 potency, and you won't be able to use it every 15s on CD, so the actual benefit is way smaller.
