This seemed to be the stance of Blizzard a while back. Why do I find myself searching for a second priest and DK for Heroic Zul? Why is it so much easier with 2 warlocks and solo runners on G'huun?
Now I am sure these fights are possible with a less ideal setup but not having the two priests on Zul just makes it so much harder that, at least for us, it seems you NEED to have them. Thing is we unfortunately only have 1 priest on progression raids and need to be lucky and get a pug every week. This all seems against the "bring the player, not the class" mantra..