Thanks for the great response. I have run the Execution Herd a few different times, it does pack a nice punch. I also recently have been running the Castellan. Being able to add one to wounds for all Legion of Azgorh models is actually pretty devastating . I have had a couple of spectacular games where the Castellan is on the front lines, and giving off his Martial Contempt so that the Artillery absolutely rain hell on a unit.
I too feel your pain, as it seems like when I take the Execution Herd, I tend to miss out on the bonus artefact (a product of my bad list building really). I agree with your analysis of the Fireglaives, so slow and a little squishy. I own about 60 fireglaives but only about 20 ironsworn, I am thinking of getting a few more to get that massive regiment discount, and they might make better objective sitters.
Unsung heroes of several of my games have been K'daai. In my games they do surprisingly well just because of the sheer number of attacks and also the 3" range. They can safely hide behind a unit of ironsworn and still swing over them. A unit of 3 has 15 attacks dealing, on average, about 5 damage to a unit with a 4+ save. They are also surprisingly fast, which leads to some nice plays for stealing objectives.
Drazoath has had very mixed results for me. He is one of the fastest units in the whole game, but he is such a mixed bag. Flames of Azgorh and Fireball both have gone off enough times for me to make him worthwhile as an annoyance. I tend to then charge him into infantry blocks; he has been able to hold off big blocks in my games, but I tend to pick units that don't have rend or high damage. I like him just as a fast unit that can sometimes get objectives, but for all of that he is definitely overcosted.
Actually re-reading my post, it becomes clear that LoA play style is essentially that the battleline (with exception of Centaurs) are very slow and typically bad at "taking" objectives, whereas all of the elites are the opposite, a waste of points for holding and decent at getting to and contesting objectives. All LoA elites tend to lack the bodies to outright steal an objective.
Still absolutely love the army though.
Lastly, it sounds like I am preaching to the choir in terms of the value of the Skullcracker. How are you considering kit bashing yours? I have been looking at maulerfiends as one option; and Empire Steam Tanks with some retrofits as the others.