I dont know if this has been suggested but with the black smith in development why not make it that the footman has to be a certain level until it could wear better armor?
This prevents that other armors become obsolete and it would make sense. An untrained rookie wouldnt go in full heavy armor when it just learned how to swing a sword.
Also if you give heavy armor a speed penalty, you get more depth in combat. Do I go for a faster defence or a more durable one?
What Do you guys think?