Exactly what Oizen said. Since GnB has a builder/spender design it suffers from any downtime where you can't generate resources while WAR gets to happily watch their burst cooldowns count down since they don't have to spend any resources on it. DRK on the other hand just regenerate them passively while doing nothing. As for PLD, I don't even know what it does, but damage doesn't seem to be it's thing this expansion.

Now this absolutely does not mean that I want this changed for Gunbreaker, having to actually execute my rotation correctly for my burst to properly work is something that makes the job interesting to me. And if downtime costs me some dps then so be it.

When I play WAR on the other hand I sometimes even end up breaking my combo when I'm not paying attention because watching the paint on my wall is more interesting, which tends to happen on that job, and it doesn't matter. Oh wow I lost 20 gauge, big deal when I get 3 Fell Cleaves, 1-2 Inner Chaos and a Primal Rend for free every burst window, only requiring me to have the cosmic brain power to press IR on cooldown.