I typically don't play AST (SCH main here), but in my dabbling I've tended to give the tank 'melee' cards when there's only ranged/casters, with the idea being more about building my 3 seals.

That said, I didn't stop to think that DPS will typically outperform tanks outside of trash pulls generally to the point that half the potency is still better spent on DPS, and may need to adjust next time I toy with AST (which will be a ways away, b/c I'm far more interested in Eden and other classes atm).