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Action cost is of course an important factor, because the fewer actions you require to deal damage, the more likely you'll be able to deal that damage when you need to. Strikes are particularly good at this, because they're so flexible that you can make several in one turn and thus choose whether to focus on one target, attack two different targets, and so on. By contrast, most spells and certain activities, like Spellstrike, are costlier and thus less flexible in this respect.
AoE is a more situational, yet hugely important component to damage that translates to a massive action economy boost in fights against multiple enemies compared to single-target damage. Because those multiple enemies will be individually squishier than if the encounter featured one big opponent, you don't need to deal the literal most damage in order to be effective, especially as those enemies' weaker saves will make them more likely to critically fail and take double damage. For this reason, it's important for the party to access at least some measure of AoE, usually through your caster, in case you run into encounters with lots of enemies.
Raw damage is an obvious factor, as sometimes you just need to deal as much damage as you can. This is particularly important when going up against resistances, as one big instance of damage will get mitigated a lot less than multiple smaller instances of damage. Spells fired from high-rank slots tend to be good at this, as do several Strike feats that let you make one big Strike with extra damage, or combine the damage of multiple Strikes. However, there is only so much raw damage you can output before you start overkilling enemies, thereby wasting your power when other characters could have done a more efficient job dealing less damage and doing something else.
Reach is quite important, because being able to damage your target from afar beats needing to spend actions to move closer to them, and expose yourself in the process. Spellcasters tend to be good at this by default, and many martials can opt into ranged builds with even greater reach than a caster.
Reliability makes a large difference in a number of situations: sometimes, you just need to damage someone no matter what, even if it's not by a large amount (for instance, fire damage to disable a troll's regeneration). Save effects and splash damage are great for this, because unless you get really unlucky, you'll get to deal that damage, and those effects can be great for finishing off targets who don't need much more damage to die.
Resource cost is a factor that crops up in extended adventuring days where daily attrition starts to kick in. Martial classes aren't particularly affected by this at all, as their damage is almost always at-will, but casters need to ration their higher-rank slots based on the amount and difficulty of encounters they're expecting to run into, and thus not expend all of their most powerful spells too early or in the easiest fights.
Stickiness is a niche, yet highly useful aspect of damage where if you can guarantee that you'll keep dealing damage to an enemy, you end up saving a lot of actions that you can spend on doing other things. If your sticky damage also triggers a weakness, this means you can deal disproportionately large amounts of damage at significantly reduced cost. Persistent damage achieves this, which is one of the Alchemist's strengths, as do several AoE spells that create hazardous terrain, generate lingering zones of damage, or can be Sustained to keep dealing more damage at a reduced action cost.
Versatility of damage types is important in a game where monsters have diverse immunity, resistance, and weakness to damage, as being able to use the right damage type means you'll get to deal more damage overall. Casters tend to be naturally quite good at this, particularly arcane and primal casters, whereas martial classes will usually need to have a backup weapon in case their main weapon isn't as effective. On the flipside, the physical damage that martial classes tend to deal the most almost never gets blocked entirely by immunity on monsters, so much as merely resisted, whereas those monsters will often be immune to other damage types like poison or fire.
So that's at least eight different factors to damage that nobody in the game can access all at once: martial classes tend to excel at damage that's low on action cost, high on raw damage, and that incurs no resource cost, with the option to pick up some reach as well, whereas casters output damage that tends to be good at AoE, reach, reliability, and damage type versatility. It doesn't stop there, though, as some spells let casters also make their damage stickier, lower in action costs (for instance, by casting a one-action force barrage), less costly in resources (again, by using lower-rank slots on a force barrage to finish off one or more nearly-dead enemies, for example), or higher in raw damage.
None of this I think really fits the typical discussion of DPR in my opinion, because all of these factors are differently useful based on parameters in an encounter that can vary greatly from turn to turn, and it's for this reason that I think DPR or any sort of average metric isn't necessarily the most useful measure of how good a character is at dealing damage. It's also in my opinion why damage that looks optimal or not on paper often differs greatly from practice: a Magus might look overpowered because of their high burst damage, but in practice that burst is often wasted due to overkill, whereas a Bomber Alchemist's seemingly pitiful splash and persistent damage becomes really scary when a skilled player uses it to constantly trigger weaknesses and stack multiple instances of persistent damage in one go.
