Originally Posted by
Extremity
Yeah, what was said above is accurate.
Basically, you can't look at 100% to 90% as being 10% of the boss health and thus 10% of your damage - consider what percentage of your overall damage takes place during your burst phases, and specifically your opener. More than any other class, we rely heavily on our opener damage. So, for the sake of example, while the first 10% of a fight is, on average, 10% of an average person's damage (give or take) we could argue that we do 20% of our damage during the first 10% of a fight due to our opener burst.
This is not mathematically accurate, of course, it's just to make a point. The fact that we have such tremendous burst at the start of a fight is one of the reasons the belt is so good for us. If we had a static rotation that was the same for an entire encounter, the belt would be a relatively flat increase and not as beneficial. Because we open with such tremendous burst, the belt becomes much better for us. Its use on an encounter also depends on how many adds there are, how much hp they have, how quickly they die, etc. There are fights where the belt might be twice as good compared to another, you really can't rely on one simcraft as an overall "this is always the way to go" resource.