I'm about 99% sure I am right (because I used light fighters a lot) when I say...
RMSS Core is none: 0%
MAC: Starts at 40% which can be lowered to either 30% or 10% using styles (not sure why they didn't include a 20% option).
So it was free to begin with and the expansion made it more 'costly'... and I'd use them exactly that way, i.e. 0% if not using the MAC and 40/30/10 if using it because each are balanced with their individual rulings in mind. Personally I think the MAC did a lot for Pure Arms users in general and, while I don't use it as-is a lot of the time, it changed the way we build them all.
I'm not sure about the other versions. If I remember correctly RMFRP doesn't even have the adrenal defense skill in the book, even though it is referenced in various charts and the index.