Come to think of it, can I ask why you're changing the weapon / armor values at all? What's wrong with how they are currently set up that you have to change it? I think this is a case of "If it's not broke, don't fix it." The other criticisms in this thread blow that direction, too.
The problem of shields again. I want them to be good, to make sense, but not to be a "must have" sort of situation. DFRPG has no rules for shields. Some houserule it as armor, others have it provide bonus to defense, etc. I think having a shield and armor is better than just armor.
I guess I should break that down:
A shield plus armor should be better than armor.
A shield should be the easiest way to boost defenses.
If one isn't going to use a shield, the offensive tradeoff needs to be worth it.
If one is using a shield and armor, one shouldn't be invincible.
For a modern game, shields are something which would be a major part of a character, so requiring the investment of stunts, etc. makes sense. Treating it on a case by case basis makes sense. In a fantasy game set in a medieval setting, shields (and armor) are going to be ubiquitous. The combat system needs to reflect this.
Heavy armor requires training (might and endurance, but I'd allow a stunt to mitigate the restriction).
Heavy weapons require strength to use effectively (otherwise you'd have power but be slow and thus ineffective).
The mean would be towards one-handed weapons and a shield with light armor. So we'd be looking at Armor 3 with Weapon 3. That's a decent balance in my book.
Investment in defense or offense would skew it, and more easily towards defense. Since stunts to boost damage are easy to make and common, it seems reasonable that we'd end up with a situation where skills are spent on defense and refresh on offense. This seems in line with what we see in DFRPG.