I'm not suggesting that she's a better overall threat generator. What I'm saying is, Khem even geared does considerable less damage per healing required.
I was literally able to handle you know who at the end, and subsequent champions today by just letting her do all the work. Her damage to healing required ratio is much better then either Khem or the 'other' tank you get later
She actually generates more threat then HK-51 even though their damage output is similar. I attribute it to melee versus ranged. Still, I tend to use HK-51 for normal dailies just because he's new and shiny, and played right you can essentially have 5 stacks up (i.e. assassinate) for any particular scenario you need it for "cc" in a heroic 2 or 2+ situation.
Of course, it helps that I'm very well geared these days in all augmented WH gear with the elite saber.
If one really wanted to use Khem, I'd level up by ascending the madness tree. You'll be able to do quality damage at level 21, and serious damage output as early as level 26 once you get death field.