It takes skill to move in heavy armor. It takes skill to change a thrust attack, that would penetrate chainmail, into a slicing attack which will not. It takes skill to do these various things. Read some skill books and you will see examples. Thats like saying if you can use a knife you can use a sword and if you can use a sword you can use a bow.
I have read about actual armor and even plate armor was less inhibiting than popular belief -
"Plate armour could have consisted of a helmet, a gorget (or bevor), pauldrons (or spaulders), couters, vambraces, gauntlets, a cuirass (back and briastplate) with a fauld, tassets and a culet, a mail skirt, cuisses, poleyns, greaves, and sabatons. While it looks heavy, a full plate armour set could be as light as only 20 kg (45 pounds) if well made of tempered steel.[2] This is less than the weight of modern combat gear of an infantry soldier (usually 25 to 35 kg), and the weight is more evenly distributed. The weight was so well spread over the body that a fit man could run, or jump into his saddle. It is possible for a fit and trained man in armour to run after and catch an unarmoured archer, as witnessed in re-enactment combat. The notion that it was necessary to lift a fully armed knight onto his horse with the help of pulleys is a myth originating in Mark Twain's A Connecticut Yankee in King Arthur's Court.[3][4] (And, in fact, the mere existence of plate armour during King Arthur's era is a myth as well: 6th-century knights would have worn mail instead.) Even knights in enormously heavy jousting armour were not winched onto their horses. This type of "sporting" armour was meant only for ceremonial lancing matches and its design was deliberately made extremely thick to protect the wearer from severe accidents, such as the one which caused the death of King Henry II of France.Template:Http://www.themiddleages.net/armor.html
Tournament armour is always heavier, clumsier and more protective than combat armour. The rationale is that nobody wants to get killed in a game, but on battlefield the question is about life and death, and mobility and endurance is a more important aspect of combat survival than direct protection. Therefore combat armour is a compromise between protection and mobility, while tournament armour merely stresses protection on cost of mobility."
Also the idea that skill is going to somehow make the armor reduce more damage makes no sense - the materials and construction of the armor are what determine it's level of protection.