With PVE Harbinger can be fun, but unforgiving for sure.
Potions as some other said feel very basic and dull. With other specs I always found myself using the other talent specs, but the potions seemed so dulled down I was not excited to really use them. Animations to it lacked quite a bit too.
Blight is to long. Sure I "can" be a true glass cannon with dmg. However using our Elixir Heal also damages us seems insane. Sure go ahead and heal, but let me take 10% of your health too. 😳
Given it would be crazy to put on everything that stacks blight, but that would go from 31k HP to 15.8k. Being realistic you would manage blight and would be in more DPS based gear. I fear going into Fractals, Raids, or World boss would be a death sentence. I would be very afraid to cast anything that gives me blight as there is no mechanism to transfer it, defense or other options.
The Pistol is not really something that feels natural. Instead what about summoning options similar to Engineer with Flamethrower, or Frost Bows etc. Let their be something evil and undead that summons forth.
Maybe a floating tome book or some sort or magic cauldron with spell animations that come from it as you cast.