The other stuff is OK. I'd prefer heavier armors to offer more PRR right out of the gate. Frankly, it doesn't need to scale by BAB either - just a flat amount of PRR would be fine.
But AC as become a pretty flat bell curve made of translucent jello. It's hard to see, hard to predict, you don't really know where you stand, you know more is better but generally speaking, everyone falls in the same range whether or not they devote lots or little investment into it. Investing tons into it, because the jello curve is flat, doesn't give a lot of value.