Hypersmurf said:
Do you feel that a Barbarian wearing Mithral Full Plate benefits from Fast Movement (Ex)? Do you feel that an Bard suffers Arcane Spell Failure while wearing Mithral Scale Mail? Do you feel that a Ranger retains his Combat Style while wearing a Mithral Breastplate?
Those are limitations of the normal versions of those armors.
Greater Ironward Diamond is not a limitation of the normal version of heavy armor. It's actually an advantage.
I understand how you are getting to where you are getting, but I do not quite understand how to explain how backwards that is.
If one were to write a computer program to handle mithral armor, one would list all of the limitations of full plate armor and adjust those limitations accordingly when applying mithral.
One would not convert full plate armor to medium armor first, check the list of limitations of medium armor, and then put those down as the list of limitations.
The word "limitations" in the rule refers to the original category of the armor, not the new category of armor. The limitations being modified by all of the mithral rules are the original limitations.
For example, one adds two to the max dex bonus of the original armor's max dex bonus when making it mithral.
From my perspective, your interpretation is a semantical game on the word "limitation". Greater Ironward Diamond is not a limitation when applied to Full Plate Armor, hence, that rule does not apply. It's a limitation to wearing light or medium armor, but that's irrelevant to whether it is a limitation to wearing Full Plate Armor. It's not.
Instead of:
List limitations of heavy armor. Adjust all of those to medium armor values as per rules.
Your interpretation is:
Adjust all aspects of heavy armor to medium armor values. Check to see if any are limitations of medium armor as well. If so, adjust them again.