Sykar
Arcane
Well, certain monsters are immune/resistant to certain dmg types, so there's that. Chaos and Aether are the only magical types that don't have a dot.
Different resistance types beyond 3-4 are just flavor. I don't remember if the different DoTs did anything special either, apart from just being, well, a DoT.
Not sure I can agree. It sure makes a noticeable difference when I am on my AAR character or on my melee Spellbreaker for example. The AAR character struggles more with enemies of the Aetherial faction, especially Flesh Hulks. My Spellbreaker on the other hand eviscerates them quite well but struggles with undead noticeably in comparison due to high pierce and cold resistances.
Agree or not, it's the truth. What ArchAngel said is true, that the only damage type that has a mechanical difference is Pierce. Otherwise it's all mechanically the same, just pick which flavor you like the most, kind of. The damage types are superior / inferior based on how the resistances / immunities have been spread across the monster roster. As I remember, physical is one of the best types purely based on the fact that there aren't many enemies resistant to it and how easy it is to access items / skills that lower physical resistance. Aether is one of the worst damage types since there are so many enemies that resist it and there isn't easy access to ways that can lower Aether resistance.
Not like that is any different in any other game and often makes even less of an impact. Case in point: D3.
Kinda sad to compare Grim Dawn with Diablo 3 which is one of the low points of the genre. Diablo 2 did the different types of damage better since they all had some kind of mechanical difference. Lightning was highly random, fire was reliable, cold reduced movement / attack speed, magic is the least resisted damage type, poison was purely a DoT and physical is the most self explanatory. In Diablo 2 you could really feel the damage type as it had a mechanical impact on the game. In Grim Dawn the type of damage you do only impacts on what gear you want to collect to increase the damage of your choice. Resistances matter a bit less in Grim Dawn as well since Crate just stacks a 2-3 different types of damage per skill so that you'll never be resisted completely, which could've been the case for a poorly built character in Diablo 2.
That does not change the fact that mechanically they were the same as Grim Dawn. What does it matter if the damage range is low or high? Magic damage was resisted and physical damage was rolled against with AR and armor similar to OA and DA here. Fundamentally nothing reallly different. Many cold spells also slow/freeze here as well, Arcanists OFF or Tozans for example or the Nightblade's Ring of Frost Transmuter, etc.