I don't see why Enhancement needs to keep Flametongue. Windfury could be made as the thematic passive for Enhancement plus Unleash Wind.
Windfury passive
Your melee attacks have a 20% to trigger two additional attacks with both weapons.
Even fewer sources of damage which is what the devs wanted. Obviously, Enhancement's damage has to go up a little to compensate for the loss of Flametongue. Unleashed Fury would then neatly buff each Unleash spell individually.