[Maerlande]

That's why I mentioned the two special cases of samurai and blacksteel. Both seem potentials for special cases.

I agree with the basic symmetry. It's pretty valid for nearly all cases and both realistic and intuitive. Most heavy armour is just plain heavy. You are including quite a bit of realism. From experience, putting on more armour (ie more mass and protection) both tires and reduces mobility. It also reduces vision which is pretty critical to defence.