I can see what your are thinking and unfortunately I think many who wish to just power play the game wouldn't go for it. One thing did come to mind though... often in my reading I hear about a sword user who has become so accustomed to their weapon that it feels as though it is an "extension of their body". Maybe your system could work for individual weapons rather than materials. Different weapons have different weight and balance, and it takes a warrior time to become full accustomed to these. So if we are shooting for realism we could see a learning curve attached to weapons, that see you rewarded for using a weapon for an extended period, and disadvantaged when picking up a new weapon and forgoing the time spent on learning the previous one. But again, I can't see this making it in.
That's what I was thinking. A dagger will be a dagger whether it is stone or steel. But if you train your entire life with an Iron Sword, switching to a Glass Longsword will feel a lot different, even though glass is stronger. But to reduce the severity of the learning curve, maybe you increase your expertise with the weapon type you are using (Say Swords), at rate X, and then you also gain expertise with the other bladed weapons (dagger, longsword, and Claymore) at a reduced rate like .5X? So if you use a Sword and gain 20 levels of Expertise you expertise with the other 3 would be at 10 as they grow half as much. This would make the learning curve much more manageable and friendly.