I thought of doing this as 5 shadow priests, but never did it...

I have a team of mages (which I spent 200 shards on the BoA shoulders for--bleh) that absolutely suck in the level 19 WSG bracket. My main "solo" character in TBC was a mage, so it was home sweet home for me. It just sucked.

Cloth + standing right on top of each other + AoE + no ability to heal = dead quick.

As far as priests, I would imagine the squisability would be the absolute same, but you'd be able to throw yourself some heals. Anyway, as a boxer you just run into a lot of AoE and cloth won't put up with it.