My take is that the Armor Specialist bonus only applies to actual AC, not to AC bonuses from another talent.
I would assume that any modifying ability such as this modifies BASE. You are assuming that it modifies you're already modified armor rating. In the vast majority of such mechanics I've ever encountered, it doesn't work that way.
Your second calculation is the correct one and I would feel safe assuming that this is working as intended. The other way would be weird and would open up all kinds of cans of worms. For example, if there were multiple +% abilities, which applies first?
Unless explicitly stated otherwise, you can safely assume ANY game mechanic that modifies an attribute always modifies the base attribute.
I'm assuming it applies to your *Armor Rating* because (again) it says this in the Armor Specialist tooltip:
"Armor Specialist improves your armor rating by 5% per point and decreases heavy armor movement penalty by 20% per point."It says "armor rating". Not "base armor", nor "base armor attribute", and not "actual AC". And your "Armor Rating" is a combination of many things including, *but not limited to*, your base armor as well as additional modifiers. There isn't even a "base armor" score. It's just a "From Gear" modifier, which is one of several modifiers that make up your Armor Rating score (along with Armor Specialist and Thick Skin).
I would also say the tool tip of "Armor Specialist" fulfills your
"..unless explicitly stated otherwise.." condition, since it explicitly states "armor rating" quite clearly.
As for your concern about
"if there were multiple +% abilities, which applies first", it's moot, because there isn't when it comes to armor.
Don't safely assume anything. Better to ask the developers and let them decide how they intended for it to work. Either way, whether it's the tooltip or the order of calculations, something needs fixing.
