Im pretty sure he added the immunes because casting is way better than meleeing, it makes alot more dmg.
Crit way more often aswell.
Easy to scale damage, and you dont need to put anything into Vita really.
I agree that some of the immunes are terrible to find when you solo, cause if u dont have more than 1 set you wont be able to kill it sometimes, or it takes like 2-3 manapools before you can dmg it.
All elements have 2 immune ones /3 for fire.... If you count the one that are immune to all elements.
This is also one of the reasons he added "mastery for the elements" to make urself immune against one element or more.
but to become completly immune and become healed from the mosters u need to get 101+ mastery into one element.
I dont remember if your prof counts as a mastery or not, but if it doesnt u need 4x items with 25mastery on each item.
= u need a glypher to be able to get there. and there's not even items to put u there either.
But all mastery gear is still resistance.
and now i have no idea what this clusterfuck had to do with ur post... xD
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O/T
If something would make the immune stuff easier solo, i'd be all down for that

But there's also maps that you could play in to skip all the immunes for your element, so it's not really that hard to avoid.