Using a Hide Covered Round Shield at 0 shield skill, 68 width, it's quite difficult to ensure a block against ranged. You'll have to use a round shield with 78 width or a huscarl or something to get decent coverage. Currently trying a round steel buckler with 9 shield and I have yet to be shot around it (likely possible, but a challenge).
Shield skill would need to be changed so it's not so lenient at 0. Maybe even make it a penalty like -15% with a scale of 15 for 1-3, 10 for 4-9, and cap it at 9 (can only get 10+ with a shield wall). Shields would need to be more expensive so you can't just pick up a super 6k gold huscarl, maybe 10-11k. Scale up strength requirements to 18-21. Shield skill should also have an effect on shield upkeep. Maybe some experimentation with shield speed > 100 could also be used with some lower tier shields and bucklers to give them a reason to be used outside of upkeep. This will make it so 0 shield skill isn't OP and provide a proper scaling to make shield skill more worthwhile. Shield skill 4 = 40%, which is the current value, then 10 afterwards until 9 shield.