Hmm. I didn't have much trouble with those guys once they were even con to me, using the same M1 charm.
My ^^^ heroic strategy is a little different from yours, however. I set the pet to use ranged attacks: /pet ranged then just have him attack. Unless my pet's mob AI is being wonky so he runs into melee range I don't usually need to back him off at all. Indeed I want him to unload as much DPS as fast as possible -- no pauses please! Meanwhile, I focus on keeping my target stunned, stifled, dazed -- whatever is appropriate -- and most importantly ROOTED. I'll mezz if I need extra time to keep root on him (or a stun/stifle on a caster). I don't cast a lot of DPS spells myself, apart from reactives. Probably I could work more in but I really focus on sticking that root because if the mob reachs me or the pet my chances for winning dip sharply.
One UI mod I've found helpful is the Othesus pet window. It adds both a /pet ranged button, and an attack button that also turns defend/guard back on -- both super handy if you find you need to reposition the pet off because your target worked his way into melee range.
Hope this helps ~Firebuck