There are a couple of considerations, but the short answer is "focus on one or two elements".
adventuringsucks wrote:Given the choice between Weapon A that does 500dps split across many types (40% phys, 20% dark, 20% fire, 20% blight), and Weapon B which does 500dps of a single element, which should I pick? It depends on how damage calculations are done in ToME4. In some games, Weapon A's damage being split across many types will make it nearly useless as dark/fire/blight are all absorbed by some mid/late game monsters' resistance.
"Damage Resistance" itself in ToME is percentage-based -- reducing the damage taken from fire, for example, by 40%. Some enemy types (e.g. fire drakes) can have 100% resistance to particular damage types. Being 100% based on fire damage can be a disadvantage there. (Enemies that are 100% resistant to physical damage are vanishingly rare, at least at lower difficulties.)
However, there are assorted damage reduction effects that have caps -- there's straight-up flat damage reduction, and then there are effects like armor which reduce damage by a percentage up to a maximum amount of damage blocked. Armor, however, is a special case in that it only affects direct weapon damage
and it is applied before damage conversion -- so if you're actually looking at a weapon that converts 20% of its damage to each of dark, fire, and blight then armor will affect the base damage the weapon is doing and
then the damage get split into different elemental types. Weapons that do that are pretty uncommon, though; more common are weapons that do physical damage and then say "+40 blight damage on hit" -- for that +40 damage the armor has no impact at all, but other forms of flat damage reduction will be applied separately both to the weapon damage and to the blight damage.
On top of that, your class may give % bonuses to specific elemental types; that should generally be considered an encouragement rather than a requirement to focus on those damage types -- you can usually get a lot more % damage bonus in a specific element from gear than you'll get from your class. However, picking a small number of damage types to stack damage bonuses in will generally be a good idea.
On higher difficulty levels, you'll run into a lot of enemies with very high Resist All. In those cases, your ability to do any damage at all depends on having resistance penetration. While there are some sources of Penetrate All, most resistance penetration you'll get access to are specific to one or two damage types and you'll want to focus on a small number of damage types for this reason. In these difficulty levels, you'll find that random damage procs from outside of your focused damage types will be useful against trash mobs but completely ineffective against enemies that are actually dangerous. Even on lower difficulty levels you'll find resistance penetration to be important for any non-physical damage you do a lot of, precisely because of enemies that are very resistant to specific damage types.