Thunderstrike - what am I missing?

[krpeters]

OK, I tried this again, with painfully middling results. What am I doing wrong?

MA Pythium, six Theurgs (1A1W2S), first 2 scripted to cast communion master and 4x thunderstrike, the next 4 scripted to cast communion slave, 4x hold.

Net cost: 900 gold for 8 thunderstrikes, which is a bit pricey, 112.5 gold each. But if thunderstrike is such a great spell, that should be worth it, right?

Result: One half are moderately effective -- killing three enemy troops and injuring another half dozen. One quarter just miss. And one quarter hit my troops, gee, thanks!

If I'm netting 50 points of damage from this, I'm lucky. I just don't see how the 900 gold spent on these mages is a better deal than having an additional 90 troops on the battlefield. This is in the early game, of course, as always I'm trying to kill AI hordes. It seems I'm just using the wrong tool for the job; Thunderstrike appears to be more of an assassination tool for powerful units/thugs/SCs than a weapon to clear chaff off the board. Am I mistaken?