- We use the weapon proficiency rules as our basis
- You can only be proficient with weapons that you have a high enough strength and/or dexterity score to wield properly. (These requirements are cribbed from RuneQuest/BRP.)
- You may not use your classes special abilities while wearing armor that is ordinarily prohibited for that class; i.e. No backstabbing, no spell casting. However, there is a chance you can get away with using Read Languages while wearing plate mail.
Upon further consideration, one factor became apparent: I cannot think of a more iconic item of the "Fighting Man" archetype than the shield. If I see a picture of someone using a shield, I assume they are a Warrior with a capital "W". Sure, other archetypes use all sorts of arms in "influential materials" and pop culture, but once a character has a shield strapped to their arm, they become a knight, a soldier, a barbarian raider, or some other kind of full-time professional fighting-man.
Of course this runs contrary to the classic D&D trope of the Cleric (think Van Helsing crossed with a combat medic); but clerics are an odd duck and more something that emerged from game play in the early, developmental days of the game than an accurate depiction of an archetype.