If you don't stand in anything, you wont need a healer. If you make it so only the tank takes more damage, then you wont bring a disc priest. They'll need balance of some sort, which lets face it blizzard has not done a good job at lately.

I don't know, but maybe they just didn't expect everyone to outgear current content so quickly. Its normal to be able to just bring extra dps at the end of the expansions, just not a month in.