8, 8, I forget what is for
Shields and polearms are both barriers that you have to get past in order to attack your opponent. Both should have a much larger impact on defense than 1 or 0 points of AC. But I doubt you could properly model that impact in any edition of D&D without completely revamping AC math.Would there be an interest in shield house rules? Basically, by making shields an active defense you remove the problems that plate users benfit from shields more than the unarmored, a reverse relationship than what it's like in reality.
Another issue is helmets, which are probably the single most important piece of armor. This at least gets some treatment in 1e, but is absent in later editions (I'm not sure about earlier editions, but the 1e rule has a definite "1e" feel to it so I suspect not).