Just combine the benefits of Martial Adept and Weapon Master into a single feat - as part of learning how to use martial weapons, the character learns a couple of maneuvers to use in combat. And whether Martial Adept comes with one superiority die or two would be a question of balance.Weapon Master I would leave at 4 weapons of your choice, but then add an ability that says Once per day when you hit with an attack from one of those weapons you may roll an additional damage dice.