Dual Wield Master

The epitome of dual wielding. Your ability to wield two weapons while fighting in combat is unmatched and you pursue the enemy with a flurry of blows that is a true wonder to behold. You may use this feat while you are dual wielding two melee weapons that you are proficient with. When active, the bonus action attack under the "two-weapon fighting" ability becomes null and, instead, this feat gives you a number of attacks equal to double the number of attacks that are allowed under the Attack Action with a -5 to the attack rolls during this action this turn. This is a kindred feat to Great Weapon Master and is intended to allow people to reasonably build dual wield characters without a drastic efficiency loss.

Example:

Level 20 fighters have 4 attacks per Attack Action. While using this feat, there is no "two weapon fighting" bonus action. Instead the fighter would have 8 total attacks during the Attack action and have a -5 to the attack rolls. 

Justification:

Assuming level 20 fighter with a +5 to strength stat- (1d12 equivalent) dmg=108/68 with average=88 while taking Great Weapon Master feat (attack action with +10 dmg and -5 on attacks) on all 4 attacks.

Assuming level 20 fighter with a +5 to dexterity stat- (dual 1d6 equivalent) dmg=88/48 with average=68 while taking this feat (attack action with -5 on attacks) on all 8 attacks.