These NPCs are swarming the bosses and killing them faster than should be possible. They are either doing too much damage, or living too easily, or Thrall is doing too much damage. Or all of the above. The fastest Azgalor kill on outland is 1:35....
This is a balance issue. Hyjal bosses are very anti-climactic when they die in 2 minutes. Like this, which is a guild's first Azgalor kill on Outland. https://www.youtube.com/watch?v=fYTVUncLyRA&lc
If you have better examples feel free to post them. I just chose these two videos arbitrarily, but they all look the same pretty much. The Azgalor fight from retail and from other servers lasts for at least 5-6 minutes, and on ours it lasts for about 2 despite him having the same amount of health. These friendly NPCs are WAY too strong and ruining the only t6 raid right now.