First - what happens when you use your first attack to knock the enemy prone. Does your overall damage increase further?
Second - with feats your damage is still lower.
Third - action surge still greatly favors the gwf.
Also not assuming maxing stat isn’t realistic. That needs included for each
1. The same thing that happens for other styles
2/3. My purpose wasn't to be better than GWF, but to balance TWF where it should be, between S&B and GWF.
Also, seeing as I did not give the TWF additional attack rolls, the bonus given by stats would be pretty static. Yes their bonus action attack would grant them a slight boost but not enough to go over GWF.
The point was balance, I strongly feel I have found a balance, without breaking the game.
TWF should be capable of doing more damage than S&B at the cost of AC. But GWF should be the primary damage dealer in terms of physical melee damage.
I don't feel the change is too complicated to implement.