There are no strengths and weaknesses (except against one skill; bosses have reduced damage from it) as all skill damage calcs are set based on stats or strict numbers. The ddamage calcs are shown for you to decide what to do, so there's no worry about elemental strengths or anythnig. The only variable is the stats involved, so skills will always do fairly consistent damage. It's more about maintaining enough supplies to last several fights then bosses!