In the not too distant past DDO realized that it was silly the best tanks in the game were monks and attempted to make AC relevant again. This change was implemented with the best intentions and you technically can make a high AC/PRR fighter in heavy armor but he will inevitably suffer from poor dps and low to nonexistent self healing. He will also find out that in epic levels his AC is no longer what it once was and be staggered by the massive hps of EE mobs. This problem of epic mob hps was addressed by indirectly by adding 3 new abilities in the enhancement pass, all of which favored monk splashes - dance with flowers to any weapon, one with the blade and earth stance available to any fighter who took kensai and monk combinations. Fighters could now purchase monk stances without meeting ability score requirements and get the best defense and offensive multipliers so once again all melee is dominated by robe wearing big stick swinging crouching tiger hidden dragon monk hybrids. This isn't a bad thing for them, after all china represents a huge percentage of the world population but it should not be the only way to fight EE mobs. After all didn't dungeons and dragons begin being based on medieval Europe? Shouldn't the knights of that era be viable? To answer this we need to look at the ecology of armor and why it dominated the battlefield for centuries.
The fall of the Roman Empire was an extremely destabilizing event in Europe and led to the fragmentation of all social order. The vast migration of Germanic tribes led to petty warlords holding sway over the countryside. These warbands would be led by the strongest most capable fighter type who was surrounded by his comitatus band. These warriors would have had armor and skill in combat which led them to defeat any unarmored opponents. Your average foot soldier of the day would have had a helmet, spear and shield and they would have fought in a shieldwall. Your shieldwalls would have been broken by the warlord and his comitatus would have had chainmail, swords and war helms. They had a huge advantage over someone who didn't have chainmail. People then gravitated to these warlords who eventually became your nobility as they provided protection for the unarmed and the feudal system took off from there.
Armor became increasingly more important for the fighting individual and well armored forces could rarely kill each other. Take a look at the battle of Hastings, Harold's Huscurls who would have used great axes and chainmail could not be killed by William's Norman knights who themselves were in chainmail and the battle was a stalemate for much of the afternoon. It was only when William feigned a retreat and the integrity of Harold's formation broke up as they went to pursue that the issue was decided. In the ensuing centuries you had warfare used a semi sport among the nobility because there was very little chance you could be killed in armor. Armor became more effective and heavier until something came along that could make it irrelevant, namely the English longbow and the English victories over the French at Crecy and Agincourt spelled the doom of armor on the battlefield. Note however that the English longbow and the eastern equivalent the Japanese daikyu took years to master and in game terms would not be lumped into a generic martial proficiency. Just because you learned to swing a sword doesn't mean you had the muscles and skill needed to use a longbow. Also note that armor didn't completely die out of the battlefield because it still had a purpose. As late as the Napoleonic wars heavy cavalry, Cuirassiers wore a plate cuirass because it gave them a decided advantage over non armored light cavalry in combat.
The benefits of armor would not only have been in protection, it is reasonable to assume a warrior clad in armor is going to be more confident and forceful in combat because he knows he has protection and ignore slashing types of attacks. If you ever watch the military channel and see them test swords on armor you can see that its very difficult to penetrate armor with a slashing weapon. An armored warrior will also have a certain degree of 'shock' value when clad in armor as he will be able to bully his way thru an unarmored opponent.
If we now look at the ddo world it is difficult to imagine how armor would ever have developed. Armor does not provide significant defense to make it worth the expense and in fact it hinders combat if we go back to the massive benefits that a warrior gets by being unarmored and a combination monk/fighter. Let us look at our battle of Hastings in ddo terms assuming William had an army of monk/fighters Harold had Huscurls with great axes and medium armor. The monkachers in Williams armor quickly furyshot all of Harold's clerics and then the better dps, equal AC, self healing monk/fighters make short work of the Huscurls. Armor would cease to be used in Europe at that point because the only way to combat monk/fighters would be with other monk/fighters. Is this the history on which the game was founded?
I do not advocate nerfing monk/fighters, the more choices a player has the better, but it must be a choice. There must be a reason to use armor that makes sense for armor to have historically evolved in the world. Currently being in armor means you lose significant dps, the ability to evade spells/traps and have access to monk stances. There MUST be a benefit and frankly it needs to be as game changing as the dance with flowers/one with the blade changes were. Some spitball ideas for increasing the benefits of medium and heavy armor.....
1. Drop the shield requirement from the stalwart defender and unyielding sentinel trees. The only requirement should be wearing medium or heavy armor
2. Take a cue form the Dwarven tree and add a % to dmg increase while wearing medium and heavy armor again dropping the shield requirement - 20% dmg increase while in heavy armor and 10% while in medium
3. Assign each type of armor a DR factor that increases based on level with a x multiplier. So while you may have a DR 10 at level 5 you DR will be in the 100-150 range at 28
4. Give all named medium and heavy armor 3 slots and restrict all cloth armor to 1. Light armor to 2.
5. Add a new epic proficiency called armored assault that gives plus 10 PRR, 15 AC and 5% doublestrike while wearing medium or heavy armor
Now we start to have a choice and we can see why armor would have developed among the martial class in our world.