It looks like you accidentally pasted the same link as the original build, btw.
The first thing that stands out to me is the lack of points in Vulnerability. When pets will be doing a huge amount of Vitality damage with all the buffs and conversion to vit, I’d invest more in that. My suggestions would be to remove some points from Hellfire, Storm Spirit, or Will of the Crypt (or a few from all three) and crank it up. Those skills add flat chaos/elemental damage or vitality% with survivability, but the %vitality RR will probably increase overall damage output more since the former skills scale in a pretty linear fashion.
Also, I would put a single point in Mark of Torment as an “oh shit” button or help against nemesis bosses.
Otherwise, I’m a fan. I’m on my phone, so I haven’t looked at the devotions yet (grimtools devotion page isn’t very phone-friendly), but something like this will be my first character in the expansion, so I’ll be using this thread as a resource.
Edit: Same with Blood of Dreeg and Aspect of the Guardian as well as Spectral Wrath. The flat damage gained by Hellfire or Storm Spirit could be replaced by that of BoD (AoE, works on pets too), and the vitality bonus with AotG helps also, not to mention the heal and resistance. The RR from Spectral Wrath will increase damage output more than the skills which were removed.
Here is a variant I came up with that doesn’t include Mogdrogen. Frankly, I think I like your constellation setup better, because losing out on all that OA from Mogdrogen might decrease DPS quite a bit, but this variation has a bit more defense with Behemoth included. I also added Manticore for flat RR.
I moved around some mastery points to include the following: Rotting Fumes (Blight Fiend) for the insanely high DA debuff (again, should increase dps much more than what is lost from removing other points), Spectral Wrath (should be 8 points with skill bonuses, as it is affected by diminishing gains after that point), 1 point in Dread for the range increase to Bone Harvest (can be skipped, I guess), 1 point in Mark of Torment for single target help and “oh shit,” and more Vulnerability, Blood of Dreeg, Aspect of the Guardian (discussed above). This cost us Storm Spirit, Hellfire (good for skeleton mages and flat damage, but outshined by the DPS gain of other skills), Bonds of Bysmiel (1 point to get the modifier, but the rest can be neglected in favor of simply resummoning if needed), Ember Claw and Infernal Breath (unnecessary, marginal), and 6 points in Will of the Crypt (that one hurts the most, so you can move some other points around to try to keep that one in tact).
All in all, with some +skill bonuses, this might change because skills like Vulerability, Spectral Wrath, etc. are affected by diminishing returns, so WotC can probably be maxed with endgame gear.