Spriest gets like 50x better when you get the talent that increases healing done from dispersion. It's literally a full heal every 2mins where you also get 90%reduced dmg and can't be snared. pretty op
Spriest is at least a B tier when i'm playin lol but for real maybe C tier haven't had anyone out dps meh. They aren't as squishy as mentioned above if you know how to move.