Weird thought that's a little off tangent but I need to get it out of my head. I've been pondering over personal armor system that I use, which isn't perfect but it's there, and passive static bonuses like fighting styles.

Something I've already considered with fighters is giving them more fighting styles as they level up. It's a pretty safe approach because they don't stack and we have enough time with them in game to understand their implications.
Most tables have a AC range they are comfortable with for their style of play and this would be an easy way for the iconic bruiser classes that are meant to take some hits can have that thematic and mechanical edge in that category without any big overhauls.