1.Why doesn't the Volcanic Plate Shield have any Elemental Defence when the Armor/Helm does?
2.If they give the Armor/Helm an Attack Speed Decrease De-Buff, why not give the Armor/Helm more Elemental/Piercing Damage Defence or a Damage Bonus to Counter it?
3.If it's Heavy, why doesn't it make a Walking De-Buff instead of an ASD De-Buff?
1) May have possibly been thought to be OP (would be a much stronger Owlite with Stun instead of Shock.)
2) The series has 'Max' Normal defense as the balance factor of sorts.
3) Something heavy can inhibit multiple aspects of an individual's physical ability. If I wore a 50-pound jacket, I wouldn't be able to move my arms as easily. Also, Ancient Plate has MSD along with ASD.
These are questions none of us have the answer to.