With respect to your question on companions, on both my healers I ran with the melee tank companion until I got melee dps; that would be Akaavi for smuggler and Ashara for inquisitor due to the issue you stated about speeding up kill times. Some people prefer range dps comps but again, its going to depend on your playstyle.
you could also try putting your tank companion in their DPS stance and put them in DPS gear. they'll kill a lot faster but still be able to take a decent beating, as well as taunt mobs off you. i have my sage's Qyzen like this. he does a lot more damage, but still tanks like a champ.
My tank toons are all shackled to the healer companion, with dps I could mix up the variety a bit more but you gotta be no top of each combat situation; i.e. I don't just use one catch-all rotation, I have specific ways I handle groups of 2,3, or 4+ mobs as well as emergency "oh crap" things I fall back on when things get out of control. I've been playing these types of games for a long time though so I have plenty of experience elsewhere to draw from.
i found that leveling with a DPS companion made things easier. my guardian tried using Doc for awhile, but it took her forever to kill mobs. Kira made fights go so much faster. even when i wasn't properly geared, we could clear 2-3 groups of mobs before needing to stop and heal. i could also solo champion mobs with Kira provided i made use of my defensive cds. i made use of Nadia/Qyzen (in his dps stance) more than Tharan when leveling my shadow tank too. though i needed him in order to solo champion mobs.