Shield skill just needs to do something besides increase durability and ranged coverage, such as:
-Improve crushthrough resistance
-Reduce bolt penetration chance
-Reduce movement speed penalty due to shield weight
Also, shield mechanics are just glitchy. Even 100+ speed shields are waaay slower to block than manual blocking, 2-handers that are like 5 degrees off center swing around your block, projectiles warp around the shield into your head, etc.