The only real problem I have with this, is that you have to focus on a single damage type for your whole party, the one and only change I really want to see is to make it so that different damage types can be used.

My suggestions would be, if Physical Armor reaches 0 than magic damage will deal 25% of its damage to vitality and 75% to the magic armor, and same other way around. The requirements to CC someone with a damage type remain the same, but this would allow teams to be 3 of one type and 1 of another.