Playing on hard, and I rarely use defensive buffs. Teleport, hard crowd control (stun, freeze), soft crowd control (terrain effects, blind, curse), disposable summoned tanks, and just generally being out of striking distance (haste + glass cannon makes you uncatchable) are usually enough to get through anything without taking many hits.
edit: Part of that is the AI, which seems to always prioritize targets by distance and doesn't seem to understand elemental resistances. Fighting a group with a pyromancer? Why shield up when you can drop a fire elemental and let him tank everything while the enemy heals him for you.
