Not many boxers at all will be main tanking raids so crushing blows dont really matter much when considering tanks, but warriors do take significantly much less damage even in 5mans than paladins and that relieves a lot of stress on your healer. Though, paladins have so much more utility like salvation, resurrection, sacrifice wipe protection, healing spec for pvp, ect, you really really want at least 1 in your group either healing or tanking.

Priest are great for aoe healing but when you gear up a bit i think pally is the optimal choice. I find priests to be great non tank healers, but they just dont match up to a decent geared pally when healing tanks. Every alliance trinity group should run a pally healer imo.