Paul Farquhar
Legend
I'm not convinced two weapon fighting should be much practical use. It seems to be more used for flash gits to show off than be an effective form of warfare (see Raiders of the Lost Ark).
Assuming no feats, TWF does the most damage at tiers 1 and 2 and Action Surge only boosts that.
Since all you are concerned with is damage I'm going to apply apples and apples.
From your figures: the GWF hits twice for 2d6+4 with 1s and 2s re-rolled, then Action Surges for another two 2d6+4 attacks (~49.3). The TWF hits twice for 1d8+4 then Action Surges for another two 1d8+4 (or 4d8 + 16, average 35) then applies TWF for a further 1d6+4 (42.5). That's a difference of 7. In subsequent rounds the GWF is doing 2x (2d6+4) (~24.5) and the TWF is doing 2x (1d8x4) and 1d6+4 (~25.5). The TWF only needs 7 rounds to catch up. Therefore if you go more than 7 rounds between short rests TWF is the superior style for dealing damage.
From your figures: the GWF hits twice for 2d6+4 with 1s and 2s re-rolled, then Action Surges for another two 2d6+4 attacks (~49.3). The TWF hits twice for 1d8+4 then Action Surges for another two 1d8+4 (or 4d8 + 16, average 35) then applies TWF for a further 1d6+4 (42.5). That's a difference of 7. In subsequent rounds the GWF is doing 2x (2d6+4) (~24.5) and the TWF is doing 2x (1d8x4) and 1d6+4 (~25.5). The TWF only needs 7 rounds to catch up. Therefore if you go more than 7 rounds between short rests TWF is the superior style for dealing damage.
As far as average damage ... I think there's a whole lot of complexity being ignored for a difference of what, 6% increase in average damage in the sample from @FrogReaver?
I get it. Some people like to eke out every drop. Just put me in the list of people that think it doesn't matter and is highly situational. Besides, there's other fun things you can do like dual throw hand axes like my now retired fighter did. It was handy and made him decent at close range.
Yep. At level 5 the overall difference is just a small percentage in the favor of the GWF. The bigger advantage that we don't have a number to really tell us is how much better it is to do damage early on in a fight than later in it. The GWF beats the TWF hands down in that critera. It's just the exact impact cannot be numerically calculated - but it is a very significant factor - and one that raw DPR numbers will always miss.