I changed up the values for generic armor. They were a bit too high:
Light Armor: +1 AC
Medium Armor: +3 AC
Heavy Armor: +5 AC
Shield: +1 AC
With a base AC of 10, a dextrous S&W Fighter has an AC of 17 with heavy armor and a shield. Much better. If I wanted, I could include a DEX penalty of -1 for heavy armor (or something like that), which would bring the value down to 16.