Am I confused, or is the initial appraisal (the average 8.33 damage vs. 7 damage) being made with GWF fighting style, but not counting the bonus from TWF fighting style?
Assuming a +3 ability score:
Greatsword without GWF: 2d6+3 = 10
Shortswords without TWF: 2d6+3 = 10
Greatsword with GWF...