Reaching way back to how armor passives worked originally, regardless of the bonus, they were based off how many pieces of a type you were wearing. There were no "when wearing 5 or more of x armor" requirements.
Now, the change to the current passive structure happened while I was on an extended break from the game, so if anyone knows the reasoning behind it, I'd love to know.
That said, if all armor passives could be reworked and returned to that original format, I would think it would lead to more build diversity and even be a vehicle to help balance.
"It is a lovely language, but it takes a very long time saying anything in it, because we do not say anything in it, unless it is worth taking a long time to say, and to listen to." - Treebeard