Until now, we have tried to preserve the tiered system Minecraft has in place for armour: keeping diamond best and leather worst. We tried to balance it by reducing the gap between these tiers, and by giving Diamond a slight drawback to use. These balance efforts have not worked, and Diamond remains unquestionably the best choice for everything except the extremely rare 1v1 in open terrain.
As such, we are changing armour again, more drastically this time. Diamond will become a tank armour: low damage, high hitpoints. Iron is becoming the damage dealer armour. Leather remains as the skirmisher armour.
The following enchants are now present on armours:
Diamond Armour applies Weakness II. You will absorb damage but not deal much with a sword. Arrow damage remains 100%, and Slowness I is gone. Archers will favour this armour.
Iron Armour applies Strength I, giving it a damage buff. In a straight Diamond vs Iron sword fight, Iron has the edge. Swordsmen will favour this armour: if you can close with a diamond enemy without taking arrow damage you'll likely win.
Leather Armour applies Swiftness I, Strength I and Regeneration I. The armour of the skirmisher: you'll be fast and difficult to kill with a bow thanks to the Regen, but are still fatally weak in a sword fight against either of the other two armours. If you're scouting or moving around but don't intend to get into a fight, this is your armour.
The above changes are designed to remove the dependence on Diamond for all wars. Diamond armour still has its place and is still slightly superior to the other armour types because of Power I bows, but an Iron wearer is now a match in an equal sword fight.
We hope this will make wars more widespread and more fun: now your success is not dependant on not losing your few Diamond armour sets. Even in all Iron your armies will stand a strong fighting chance, even if they are slightly more vulnerable to arrow fire.
I leave the thread open to commentary.