Eh, looks like you need to set the party up in tactician to do one type of damage. I got physical damage dealers that complement each other and have phys-armor check debuffs. The mage can be a summoner, necro or hydro healer in that kind of composition. I haven't done a mage party but I assume you wanna go heavy on magic damage so you crack their magic armor in the first few turns then CC them afterwards.
That is kind of what this kind of armor system causes in pretty much every difficulty, you just feel it more in Tactician.
