It doesn’t make much sense that a great sword, great hammer, as well as puny dagger all do 1 damage to shield in case of normal attack. Besides, I don’t think you can actually use sword or hammer to “split” a shield.
Maybe shields should take different amount of damage from different weapons when you block normal attacks, and “Split Shield” should be axe only skill (I don’t know how to modify it so that it could actually be useful in this case)? Or get rid of “Split Shield” altogether.
Also shields could take less damage if they are metallic (orcish).