super heavy armour of multiple layers of metal?

[Dan Howard]

I think you are over-estimating the weight of mail and plate armours. Often if mail and plate were combined then each component was made lighter than if one was the sole defense. A mail shirt worn by itself might weigh 15-20 lbs but mail intended to be worn under other armour could be as light as 8-10 lbs. Total weight would be well under what a modern infantryman is expected to carry. Armour underpadding is also a lot lighter and thinner than padded armour that was worn as a standalone defense. In some cases no padded undergarment was worn at all - the mail would have a lightly padded liner instead.

FWIW mail by itself is an excellent defense. It was the preferred type of armour for virtually every metal-using culture on the planet for well over a thousand years. Plate is better protection against blunt trauma but that is about it.
http://www.myarmoury.com/feature_mail.html