Their AI just never works the way you'd expect/want them to, and even then it's difficult to find a bless that really helps.
For the AI, you can set them to fire, it's just that the range is really short so they have to be pretty much on top of the enemy for anything to work, and as Agartha you usually want to be further back. A line of blessed HP-bags up front with stone throwers behind them is a substantial battle force. It's not really viable in actual play, since it's expensive as all get-out (and vastly inferior to olms+chaff at similar gold expenditure and no bless) but there's always single player.
Does fire/death blesses even effect boulders? Those or air would probably be about it. Well... actually, blood would help, too, for the strength boost, wouldn't it? I could sorta' see a blood bless with a couple strength of giant (or whatever) casters sitting in the back line bumping their range up.
'Course, blood doesn't exactly bring much to the argathan table (except blood stones, anyway), but still... maybe a disciples game with a blood-capable subordinate leaning on your god for heavy rituals/forging?
F9BxAx would be the classic bless, inasmuch as there is a classic bless for such a fringe strategy. Blood helps for range, but the range calculation is not very generous. In my opinion it should be STR/2, not STR/3 to make them viable. Agartha has a good set of options anyway, since the cave patch, but it would be nice if some of the older options worked a bit better.
Blood Stones are a substantial advantage, and having access to them is potentially worth the small amount of blood dabbling it takes to get them if you want the bless anyway.
Aside from fire not affecting ice weapons, fire/death blesses affect pretty much everything.
Not mind blast, which is pretty significant. If it did, Olms with F9 would be lethal as all hell. Or D9, since Agartha likes big D a lot anyway.