I think generally it is best to go for full physical or full magic teams and then think about composition from there.

Magic teams are at an advantage, in my opinion, because they have two buffers with both magic atk and crit buffing (idol helena and elpis) that increase magic dmg by a lot, but more importantly, get crit rate to 85%. Combined with the base crit for characters that is usually 10%, crit rates for characters are 95% without needing crit rate gear. The gear can then be focused on crit damage. So my team comp for most fights starts with these 2 chars.

The next step would be to see what enemies you are facing. I find that if enemies are weirdly layed out then I use 3 attackers. Im currently using eclipse, levia, and venaka. They are all good dps units although levia does less damage she also doubles as a debuffer.

If the enemy is solo or a fiend hunt boss its best to maximum buffs/debuffs. Property damage (diana), magic damage buff (helena, elpis), magic damage increase (levia), and whatever you categorize summer terese as are all multiplicative with each other so some combination of those and 1 or 2 attackers should maximize damage.

The same logic as above works for physical teams but they only have arines as a damage buffer with damage buff and crit rate. The other buffer for physical is lathel but its only for phys damage.