Soulmonger is only amazeballs if you’re using a Feed the Demon build. For a Fracture build, it’s roughly equivalent to Impassive Visage (though stronger in M+ than raids due to on-death souls fragments).
This biggest problem with Soulmonger is that it only lasts 3s, and it doesn’t stack from multiple souls (new souls simply refresh the duration and absorb to its original duration and maximum). If you consume 2+ souls at the same time, which is extremely common in a Fracture + Gluttony, the additional souls grants nothing at all.
This more or less innately halves the benefit of the trait. However, the trait itself is balanced against Impassive Visage (widely considered the best tank inner-ring trait) as long as you have a soul consumption event (any occurrence of 1+ souls consumed at the same time) on average every 4.0s. With a FtD build, you’re consuming a soul every single GCD (Shear spam ftw…), which makes this trait broken strong.
For a Fracture Build, you’re consuming 2 souls at once every 3 GCDs, on average, with occasional additional inefficiency from double-tapping Soul Cleave back-to-back. 3 GCDs in 4.0s requires only 12.5% haste, but the losses from double-tapping will increase this required level somewhat. However, in general, Soulmonger can be considered more or less equal to Impassive Visage, for a Gluttony build. For Spirit Bomb builds, this is halved again, and thus the trait is, of course, complete garbage, but Bomb builds have largely fallen by the wayside.
As for the engineering helm, it depends on the trait you take. Personal Absorb-o-Tron is tuned slightly weaker than both Impassive and Soulmonger baseline. However, the engineering helm is RPPM, and that probably scales with haste (though I cannot find any definitive information on that). If it scales with haste, it comes in ahead by a solid margin, even if at the same itemlevel.
However, Personal Absorb-o-Tron does have a couple of notable mechanical weirdnesses, the most noteworthy of which being that it can and does pull extra mobs if it spawns near them (rather significant in M+). It does, however, appear that the absorb is implemented as a damage redirect to the robot, and thus will absorb even overkill damage from a single attack (ie. if you have a shield for 50k, and take a 200k hit, 100k (50%) of that is transferred to the bot, and the bot absorbs all 100k in a single hit, dying instantly but not transferring the 50k overkill back to you). This makes it stronger against larger hits than many smaller hits, however, so probably better for raiding.
Auto-Self-Cauterizer has the same proc rate, but is tuned at 60% the strength of the Absorb-o-Tron, and can also proc when you’re already at or nearly at full health, wasting the effect, so it’s basically worthless.
So, the TL;DR is that the engineering helm is probably worth it, but only probably, and only if you’re willing to deal with the bot occasionally pulling extra stuff when it spawns.
