then you must be doing something wrong...cause even before end game, my guardian and her Kira would kill 2-3 groups of mobs before needing to stop and heal up. i never even used Doc. Kira just made things so much faster. now that i'm level 50 in BH/Columi, and Kira's in Tionese/Columi, we just steamroll through everything and barely ever need to slow down and take a breather. she just kills things so fast while my guardian is a taunting brick wall. it's ridiculous. i shudder to think what kind of wrecking ball she'll be when i finally get her in full BH.
Gear makes a world of difference on companions.
I am still a fairly new level 50 Bounty Hunter: Powertech tank. I just upgraded my healer (Mako) and my DPS (Torian) in Recruit MK-2 armor and the difference is honestly like night and day!
It nearly doubled my healers heals, and my DPSs damage. It also made the quite sturdy in PvE doing daily quests and soloing heroic +2's with them. (I have no problems doing them solo now with the MK-2 armor on them.) It is a rather steep investment for a fresh level 50 to gear up 2-3 companions, as each set costs around 350k credits.
My wife did the same thing with one of her DPS companions (Vector). Together we were able to duo several of the level 50 normal mode flashpoints. She is an Operative Healer with a DPS companion, along with me tanking and using Torian as DPS, we were all in Recruit MK-2 armor with 1-2 pieces of rakata from daily coms.