Well, my suggestion is to cap resistance at 100% (immunity), and create talent(for example "Fire infused"), which allows you to be healed from fire attack if your resistance is above 100%, but it would also lower your resistances by 30% against opposite element (fire/water), or lower all your other resistances by 15%.
This talent should probably require high level in specific skills (pyromancer level 4?)
Seems most "notbroken" this way
