I'll repost what I posted deep into another warrior thread a while back.
Onslaught (while really fun to use!) is just stupidly designed, and that stupid design influences everyone's ideas of how it should be balanced as well. Like brutal swing('s replacement) is now, it should have no place in any rotation. It is a very thematic reactionary movement ability that should be used to let the warrior hurl himself across the battlefield at will.


I would change it in the following way:
- No cost. A BG cost on a reactionary ability screws up the rotation and it's worthless in any serious content even if you did make up the immediate potency loss.
- Same(ish) cooldown.
- Make the damage miniscule, like 40. I'd say none, but the animation indicates at least some damage. The next point deals with this.
- A minimum range (6 yalms?). This prevents that 40 dmg from having any effect on your rotation, which the devs rather stupidly tried to solve with the BG cost. No one is going to take the time to run back and zoom in again for 40 potency. The range can be adjusted to insure it would always be a loss.

There you go, now the warrior has a thematic charge ability that is only used for movement instead of a useless ability just sitting on the hotbar annoying us. That's Shake It Off's job! Bonus, it can be used to charge INTO combat! And maybe even give back some of the Warrior feel you bungled up so badly in 4.0.