The player tends to lead off with it or do fancy placement so as not to catch allies. And you don't want to use it on anyone who's engaged in melee combat anyway, because the next damage will negate it, so catching allies basically never happens.affects everyone in the cube (also allies, so you need to cast it before melee is joined),
Which means that the PCs basically get a surprise round against any allies who are busy snapping their friends out of it. I've tried having them do that and it generally still is a massive boost to the PCs.and you can be snapped out of it if an ally uses an action.
Hmm, maybe I can give the glamour bard's charm-breaking ability to some monsters as an extra option.Last, but not least you can always modify or ban a spell if you feel that it's too powerful. Let snapping someone out of the spell be a bonus action or give the affected creature a save at the end of every round.
These particular druids didn't have conjure fey on their spell lists. But I'll keep that in mind for next time I design my own antagonists.Druids also get conjure fey. Fey have spell resistance. The druids could simply clear off and let their fey do the fighting.