Chainmails are in opposite to what most MMO devs seems to think actually both heavier and harder to move in than a plate mail. In have been proved again and again (if you want to see an example, see when they test them against each other in “The deadliest warrior – Jeanne Dárc Vs Wilhelm the Conqueror from a few weeks back).
Chainmail and platemail represent 2 different technologies and generally are chainmail primitive and offers a lot less protection. Platemail is a evolution of it that offers greatly improved protection and better movement. I own a chainmail myself and have tried out plate as well.
And yet in MMOs chainmail is a lighter armor often used by rogues or swashbucklers side by side with warriors using plate mail. It makes no sense whatsoever.
Sure, the Romans had both a breastplate and chainmail armors but the Roman breastplate were a lot more primitive than the 15- early 16th century plate armors that MMO plates are based on.
Why do some classes have acess to chain armor but not plate? It just makes no sense.