I think the definition of useable is too fluid for you to outright discount combinations you don't like. Let's say I want my Mage to use shields but I don't want to invest too much into strength. Shields req start from 6 str up. If my armour provides me with 1 str, that's one less I need to invest into my build to use a shield. In fact the armour alone is enough for me to use a basic shield.
