This would help make a difference between the armors, as right now they are pretty much exactly the same except for the bonus stats on them.
Would also make hybrids more interesting.
Leave med arm the way it is. In the middle
Give light armor:
haste/move speed/dodge boost
armor/defense reduction
Give heavy armor:
haste move speed/dodge reduction
armor/defense boost
This would add an element of realism to it (I know I know fantasy game, blah blah blah) and like I mentioned earlier make builds more interesting.
At the same time (and probably a different topic but will slot it in here) make the armor bonus (melee/range/sorc) not tied to the armor class. So we could see some light armor with melee bonus, or heavy armor with sorc bonus. This again would have a huge impact on hybrids and allow for alot more freedom.
Leave the current sets how they are (to change them after people have put in countless hours for them would be bad), but if/when adding in new crafted sets (please do this!) have a slot, similar to gem slot, where you can slot a shop bought item (or droppable?) that will determine whether it is melee/ranged/sorc based armor.
