In the past at level 34, 8WM still gave you 175wpf and 9WM gave you 183wpf. Agi was still great back then, but the bonus from WM was poor.
I think a problem that's larger than preventing agi builds access to the highest end armour is the fact that you can easily get 50-60+ armour off of equipment that should be very light. My 15 strength build uses what I consider light armour with mail mittens and a druzhina mail shirt, and even just that amounts to 50 armour total. I find that more broken than being able to wear coat of plates or heraldic transitional (even though that's a part of the problem, too). Increasing armour difficulty is a small part of multiple changes that should be done. Increasing armour difficulties by itself isn't really going to do anything except force people to switch to the lighter equally viable equipment.
Armour would be in a nice spot if gloves didn't give so much; they should increase attack power instead. Armour should scale to 27-30 strength, even though I know many will disagree. I may have the minority opinion on this next part, too, but I think IF should scale better while penalizing 0IF (could also work indirectly with the lowering of armour). Strength only has PS and partially IF that can even be ignored, while agi has both WM and athletics (which both also help increase damage) at full utility. WM used to be just as bad as IF, but now IF has some catching up to do.