Faun spell spamming

Spell spamming from mobs and players alike should result in diminishing returns. For example some kind of very temporary resist to spells like root and mesmerize especially. As far as I understand, this is the plan. So is this an intended mechanic that has not been implemented yet? Perhaps this experience can be insightful to tweaking PvE to make it more fun and meaningful.

Fauns have always been my favorite mob to fight because they cast like people would in PvP, but I think that spam should be addressed here.