Well, I'm back after a long break, and I bought the SoD pack to catch up. Now at this point I'm almost 76, and was curious if the tank merc is actually capable as a duo partner. Any help would be appreciated.

Lower levels, yes. I did some charming with the merc tank, never had to heal much, just blew stuff up, that was in the 66-70 range. I tried some kiting stuff with the merc, that worked ok. But, that was beta. Sadly, besides the low leveling testing I was doing, from 1-85, I did not use the tank merc much. To busy playing mob chasers.

It does help you solo things you wouldn't be able to otherwise. Grinding will always be quicker soloing than with a merc though.