i think medium and heavy armour should be split evenly between the low and high tiers of both dex bonus and str requirement armours, as it stands heavy and medium armour are essentially just two equal but different progression tracks based on if you favour str or dex,
put hide, chain shirt, scale mail, ring mail and chain mail into medium armour and spiked armour, breastplate, halfplate, splint and plate into heavy, that way heavy is actually an upgrade to medium no matter what stat you're using for AC.