[quote=HazmatMedic]
Knights in full armour can backflip! How the hell can I GM a balanced and fair game when I know light armour isn't worth crap? Any variety amongst armours will result in defeat! It isn't worth the risk.
[/quote]
Full armor isn't always an automatic win. Take the Battle of Halmyros, for example. The Frankish Greek knights were defeated by the lightly-armored Catalan Company. The knights were bogged by the wet ground in between them, flooded by the mercenaries. This greatly reduced the cavalry charge's effectiveness, while the Catalan mercenaries were able to whittle them down with missiles and fight them while disadvantaged. All while wearing relatively little in the way of protection compared to their adversaries. 

Tactics > equipment.