A bit ago I was running ice magic+mentalism and when the highest zone I could do was Rahu/Ilmari, it rocked. Once I moved to Gazluk, it's possibly the worst combo imaginable. It felt like everything was resistant to something I did! But I think thats fine. Its a hard rock-paper-scissors balance that I think I first noticed in the Carpal Tunnel. I agree with the player knowledge thing, that its kind of untouchable. But I do think immune and resistant can be wiggled if you do choose to switch anything up. The solution I kind of expect to be taken is having ~2 options for zones at each of the pre-100 levels with different resistances being used.

I do like the idea of having fire magic being balanced by having its resistance being more common place. But if darkness is in the same boat, I'm not sure that the balancing it around mob resistances argument makes sense. Just b/c darkness can't deal anywhere close to fire's damage, unless there is going to be a "darkness magic" skill, which sounds metal.