What about directional resistance?..
armour at the front having more than the back and both having more than the sides,

this could allow a crafty player to overcome a cumbersome yet tanked player.

It would also allow a player to go up against a dragon but wouldn't provide any resistance against lava ( as the heat would cook the player from the sides even though he'd be protected from the front and back.. not to mention the head and lower part.. )

This system would work for shields too.