I'm aware Khem is a tank, hence the reason I was surprised about how well he was doing at being a DPS. But I guess that's because the planets before Tatooine are lowish level planets. Anyway, thanks.
Companions are relatively more powerful vs content at lower level. As level scale, both your abilities and the enemies you are fighting raise significantly (a step up on tatooine, and another on Hoth)
But make no mistake, even if you outfit khem in Vindicator rakata gear at 50, Ashara's going to nuke his dps naked, pretty much.
I personally like melee dps as a tank, since you don't have to run after the mob if he pulls, and the dps she makes is slightly higher than andronikos's from people parse report.
Either works well tough.