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.
I always found the melee tank companions to lack survivability whether in tank or dps mode, especially if aes are involved. But again, to each their own. I have 8 50s, and a second agent I leveled through to record the story so my methods obviously work for me.
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.
My shadow hit 50 the first week of January, he was my first toon from early access and I finished the class story at 47. I then did Ilum and Belsavis to cap him off. Survivability goes through the roof when you are fully spec'd tank and use a healer, in the case of the shadow stealth allows you to bypass any extraneous npcs along the way to your objective as well. Nadia is a glass cannon and Qyzen had zero gear on him at that point so for me, it was much easier to use the classic tank/heal combo and push through doing content that was 2-4 levels above mine (except trying Stark at 39, that was a mistake).
So Arvaliz, as I mentioned you need to find your playstyle and develop according to what's easiest for you. There is no singular correct path in this game and that is part in parcel of what makes it shine with respect to game mechanics.