Although I like the Shield Class (SC) system I came up with. My original goal was to rationalize the rules not change them. I was trying to make the OD&D rules work as written. Or at least the Swords & Wizardry version. I may still use the idea in a home brew rules system and I welcome anyone else to do so as well.
Taking another look Armour Class (AC) and what it could actually be, I realized that I need to look at hit points as well. If hit points lost in fight are not actual wounds and instead are bruising and fatigue. Then AC is not preventing you from being hit, it is protecting you from deadly wounds. In other words being armoured give a character acess to their hit points. It converts deadly wounds into fatigue and bruising. The shield is rated so low because it doesnt prevent fatigue loss. The impact from a hit carries through and causes minor damage like bruises and tires you. Its a big target and easy to hit. And hit points are not real damage. Of course there are some holes in this idea that need to be dealt with. Missile weapons and AC for unarmoured characters. Normal clothing could offer some protection and you are assumed to be fighting back and not unarmed. Non pentrating arrows can cause bruising. Also does Cure Light Wounds work on characters with positive hit points? If you think of the CLW as a general cure all spell then it does. This idea does allow for armour piercing weapons like firearms. For example, say any character dies at neagtive 6 points plus or minus constitution bonus. Firearm damage takes characters from zero down into negatives becuse its actual damage. Circumventing the function of armour. Another way to look at it is that every attack "hits" and you roll to wear down your target. Of course that also alters what a to hit bonus is (its not accuracy anymore).
It not perfect and logic. And like most rules it might not bear up to close examination. But it is workable I think.