My input on DRK changes

[TouchandFeel]

You'd probably want Delerium to increase the target mob's vulnerability not reduce it, otherwise you would be buffing them with your attacks and any mages in your party would hate you

Edit: unless you were meaning that it gives a buff to you that reduces magic damage you take. If that is the case then that would imo be worse than INT down because it would only affect you and not reduce damage for the whole group.