Try to let everyone have 10000 HP at least. So that you can survive the non-Overstrike attacks boss uses. With the Wards nerf, you'll see more bosses damaging you for 9999.
ATK/MAG stat just helps for the first few seconds of the fight where buff/SBs are still being prepard. ATK softcap is already low especially when you factor in Magicite Passives. Elemental boost's value will reduce over time as more powercreep, fight mechanics, new elemental stuff diminishes the boost.
So yeah, HP as main priority for the long run. My healers still need 3 HP Boons after max Water & Magia.
3DS FC: 2809-9061-6615 JP FFRK (QT3rB): All utility except Runic and Astra.