They do, but their "shtick" is unit preservation: all their units have regenerating shields, and their units generally have high health/cost. Some of them have

They do, but their "shtick" is unit preservation: all their units have regenerating shields, and their units generally have high health/cost. Some of them have additional protective abilities, like the Sentry's damage-reducing aura, or the Immortal's Barrier. Finally, when raw shielding/toughness isn't enough, many of their units are quite mobile, allowing wounded/deshielded units to retreat.