One of the monk henchmen in Factions has Signet of Devotion, and everybody complained how she did such a crap job because people died while she was using a 2 second cast signet. I seem to remember that there was an update along the lines of "monk henchmen now use SoD more wisely". Perhaps that affected it in some way?
And no the heroes don't like enchantments with upkeep. It's hard for them to manage their energy that way. I even saw a wammos give his assassin hero Live Vicariously and Essence Bond, and I see the hero casting and casting it over and over, and of course cancelling it inbetween...... on other people in party. Doh!
Personally I am glad there are at least some things people will need a human for, rather than heroes knowing how to do every build.