When the player have reach maximum armor rating by smithing and armor skill perks, shield usage lost it's significant. It is because the main purpose of using shield is to block damage, if the player have reach the maximum protection just by wearing armor, why need to use a shield?
If shield purposed is to bash, we can bash without using a shield by using any weapons. If the purpose is to block elemental damage, the player with high magic resistance don't need shield for that.
So i think maximum armor cap should be toned down to 50% maximum, this making the use of shield have it's significant. To balanced it :
i. give bullet time movement ability (similar in archery) in two handed weapon skill perk
ii. give blocking ability and bullet time movement ability (similar in archery) in dual wield skill perk
ii. remove bash for two handed weapon but replace it with knockback and stun in two handed weapon skill perk to differentiate it with shield bash in which cause stagger effect
By this, the usage of shield have raised it's significant and making weapon and shield warrior game-play is different than two handed weapon warrior.
Shield warrior have more protection but less damage, two handed weapon warrior have less protection but high damage with knockback and stun ability, and dual wield warrior have less protection but very high damage
*** I first posted this in Skyrim forum, but it being blocked, the mods can just transfer it here but, whatever