Armor really does slow you down as a matter of physics. You have to overcome a lot more inertia, even with we'll fitted plate.
I would like to see full plate restricted to horseback for the most part. It really wasn't designed for long walks.
Also, a plain chain shirt hurts the shoulders, but it can be supported by attaching it to stiff leather. Think about a cheap backpack putting the weight of your books on your shoulders compared to a good pack with best and waist straps and also hiking packs with frames. Any armor can be supported.
Make the ability to dodge a function of agility, and DR a function of armor. Then make sure armor reduces dodging ability. Full plate and packin steel mod for BG handled this reasonably well. PE could do it better.
I like that shields could reduce the chance of being hit, but they make dodging harder too. Evasion of larger stuff (explosions) would suffer.