Inquisitors vs. demonologists vs. archmages

[dashcunning]

I keep thinking about using archmages but I'm always held back by the fact that they do completely terrible damage, the worst in the game in fact (in terms of damage per leadership). Even assuming 95% crit and the double attack ability, they are still only average for range units and about 10th worst overall.

Is the magic shield ability that good? It seems a waste to dedicate 1/5 of your army to a unit that's really only useful for that purpose. I haven't used them so I honesty have no idea how good they actually are, they just seem so awful.