This is one of those examples where Larian followed the source material TOO closely. IMHO one of the things I never liked about D&D is the AC system (and I started with THAC0 so I've been doing this for a while!). Yes, plate armor is heavy, but to claim that having a higher Dex while wearing it does nothing is hot garbage. It's a design choice to simplify the game, plain and simple. The same as 'one night of sleep heals you from death's door to full.'
ALL armor should work on a sliding scale of 'avoidance/deflection/reduction.' Sort of like Heavy Armor Master only less effective for lighter armor. Also, some armor should be less effective against some types of damage (slashing at plate armor would be largely a waste of time). However, once you start down that rabbit hole you now need enough new mechanics that you essentially don't have D&D anymore.
