I ran into a pack of these, recently, got to see what they are capable of. I'm assumming they are high ranking clerics, I'm fairly certain at least a few of them cast Destruction (8th level spell) and a number of them summoned elementals (7th or so level spells). So I'm guessing they are at least level 15 or so clerics.
The loot though... what they had was pretty pitiful. The most valuable item money wise was a pair of travellers boots. Considering the power, and comparing them to the roughly equivalent level NPCs in a few other places, the challenge seems kind of overbearing for what you get out of it.
Not that I expect every monster to drop a fortune and fantastic items. But a supreme Lysaga warlock should surely have something more interesting than a fashionable cloak and a scroll of grease.