I get the feeling things are getting way to complicated ...
The logic behind armor is that: Good armor is made of a strong kind of metal, but this kind of metal is heavier too ... so that's the reason why good (metal) armor should have a strenght requirement.
But what about an intelligence requirement? People who want to concentrate on magick will probably put points in intelligence ... So maybe there could be a simple cloth tunic ... but with a special kind of spiritual armor on it. It doesn't weigh much because it's made of cloth, (so no strenght requirement) but a warrior with a head of wood will never figure out that this is a special kind of tunic so he can't wear it (an intelligence requirement).
You could even go further (but maybe not good for gameplay). In

there were special pieces of armor with special bonusses like strenght + 2 or with a certain skill bonus. I guess just identifying such an item is not enough to use it, you need some intelligence too. So maybe only chracters with a certain intelligence can use such pieces of special (enchanted?) armor. That way a magick character can still have some benefit from investing in strenght ...
Just some ideas ...