So I keep seeing items that say they do magic damage (like the early game Wisewalk boots +2 mag dam (fire, ice, holy, lit, earth)). I don't get this. Is this a total of +10 dam, but anyone with Resist All of 2 or more nullifies the whole thing? And how does resistance work with this? Anyone with a resistance of 2 makes this nullified as well? What's the advantage of these items?
This is +2 Damage of 5 different types. That means that resistance will very quickly chew that up, if you aren't finding ways to reduce resistance or buff this damage in other ways. Most monsters have low resistance. +2 is probably going to result in 0 damage on most days, if you don't pair it with any buff / curse / gear.
Ah, I see. Even in the endgame, I only see these items being around +12 or so, meaning that without the other gear/curses/buffs, they are fairly useless on their own. Add everything together and they make a nice addition to damage, but without a specific strategy to utilize them, they're not worth much. Right?
I would say that's fair. This game requires a solid group build with clearly defined goals and roles for your characters.
If you're using Strickening and or Torrent of Steel, you'll see much more use of this type of item. Unless you're affecting enemy Resistance directly, I wouldn't focus too much on building magic damage.
Monsters have low resistance, you'll see that it might not pass 10 for some monsters throughout the game. So, +12 x 5 will impact extra damage, but if you are doing nothing to compound that strategy, yes its pointless. But I'd say that about most strategies in the game -- if you're just trying to do something standalone without support from any gears / buffs / curses, you're doing it wrong