I am no expert in this game, so if i am off base, please correct me. I have a Necro/lock/archon. The thing is a beast to solo with because of soul purge(which i firmly believe is the most op'ed skill in the game,as long as you have charge,you just can't die). Now, on my necro, my pet holds agro just fine on 1 mob, but more than that and it is a **** shoot. The only reason i stay alive and my pet stays alive with more than 1 mob is because of soul purge, but that costs charge. Now, again, i might be missing something important here, but your build does not include soul purge. Which means you and your pet with die, eventually(or you will bleed yourself and your healer dry of mana so fast, he will kill you). Your build is good for dishing out damage and has some ok heal returns, but, you have no defense and no way of mitigating damage, and you didn't take radiate death/Neddra's Grasp, which i would think you would need since you will have to hold agro through damage, so you will need all the AoE you can get.
Now,again, i could be way off base and missed something important,but, if you are going to have your pet tank, you will need soul purge because you will drag agro from it eventually and SOul purge is all that will keep you alive. To be honest, the elementalist pet seems to be a much better 'tank' than the necro pet. In my limited experience, NONE of the pet classes have 'great' tanks. I have tried the necro,elementalist and rogue, and all of them have failed to hold agro when there is more than myself dealing damage. They are great to solo with, but more than one person pew-pewing the mob will pull agro from them so fast it will make your head spin. Having said that, I have witnessed a couple elementalists tanking elites to pretty good effect with their Rock Golem, but they end up most of the fight 'healing' their pets while everyone else kills.