I'm okey with these changes if heavy armour then actually helps make tanks survive in PvP. So at least double the mitigation armour provides, so a set of heavy reduces damage by about 60%, (buff boss single target damage to compensate of course) and make sure the extra damage from light/medium armour only applies with 7 pieces of the respective armour so you don't end up with high damage builds that use 2 major heavy pieces. Also, as a heavy armour passive, 7 piece heavy armour should make you immune to light attacks unless its a crit.