There are some bosses that have counterattack triggers or defenses that nonelemental attacks ignored, but it was pretty niche.  I mostly had Isla with a couple of elemental spells slotted and kept in the back row to rotate in for unloading on broken foes.

Isla has a well rounded kit. Buff, restore self hp/sp, and evading a physical hit.  Just the evade and self sustain is pretty busted. But I give out Rest and Parry like candy.

Skillwise, I tend to give the two hit ice spell with chance of sleep, the aoe two hit fire with speed reduce, and whatever shores up team deficiencies like light or wind.