Mirrorrorrim
Hero
Because not everyone benefits from weapon mastery. Why would a non-warrior with martial weapon proficiency ever choose a greatsword over a longsword if both could deal 1d12/2d6 damage?The greatsword or greataxe would also get a weapon mastery along with the damage. Flex is a weapon mastery, so if a versatile weapon was used two handed, the user would have to choose between flex and whatever else was the option, so why not?