I have been curious about this for awhile. The newest event made me even more curious because on level 25 crystal cove I was able to reliably land mass holds, charm monster, and make them dance in my disco balls.
I don't have a ton of high end gear, but my enchantment spell DC is 40 and my necro spell DC is 38.
I went into the devil battlefield to check out my wizards effectiveness in enchantment / necro spells before the event. I found that my spells did not land as often as during the event.
Is the spell DC required higher then a level 25 quest?