This bit seems to be incorrect. You should fully calculate the probability before applying the damage. The calculation for each attack in the Attack action should be (1 - (1 - 0.6975)^2)) * 15.5) or 0.91 * 15.5 = 14.08 so the damage is (2x 14.08) + 8.02 =36.12 eDPR. And yes, Gaudere's Law probably does apply.
Can't do that for this case, because the damage expression is different. Without the fighting style, the off hand damage is 11.5 avg per attack.
BTW if you really want to cheese out, run the numbers for the 11th level Paladin with one level each in Fighter and Barbarian.
Assuming base accuracy 65%, not counting crits, it's 52.7 > 50.0 > 45.0 for PAM/GWM > DW > GWM only.
I think I need to adjust the fighting style. I didn't really want to, but it scales too well and is too good compared to Dueling/GWF. Maybe just a flat +2 to off-hand attacks, or stat mod to off-hand attacks made during the Attack action only.
Suggestions: the re-roll be made without Advantage and only once per turn.
Not allowing the reroll to gain advantage is something I've been considering. The thing with Advantage any my DW rules is that it's inheritly limiting; the accuracy you gain on the follow-up attack is mostly canceled out by the decreased chance of needing the follow-up attack.
And the issue with once per turn is that it doesn't scale with multiple attacks. Dueling style, GWF style, SS, and GWM all increase in value linearly with number of attacks, I'd like a DW fix to do the same.
BTW pity the poor Duellist with a shield and spear and Shield Mastery and Polearm Mastery. Either she uses the Bonus Action to gain Advantage or for the butt attack given by PAM. All for - combat-wise - a base of 1d6 + 2 damage (2d6 + 4 at 5th level) and +2 AC. It really shows the power of damage adds.
Oh, I do. I wouldn't mind seeing an offensive feat that could synergize with Shield Master to give SnB some punch. I mean, it needs less punch in exchange for its higher AC, but it should be like a 20-25% decrease, not 50% or more.
Assuming your baseline accuracy of 65% the 16 Str 5th level Duellist with SM and PAM gets (2 x ((1d6 + 2 + 3) * .65)) + ((1d4 + 2 + 3) *.65) or 2 x (8.5 * .65) + (7.5 *.65) = 15.925 damage. Apply advantage from SM and damage drops to (2x ((1 - (.35 ^2)) * (1d6 + 2 +3)) = 14.92. Note that she does in an entire round roughly what the Barbarian does in one attack. And the second calculation assumes that Advantage is successfully given, so average damage will actually be less.
Hmm. Let's test this add to Shield Master: "When you make an attack with a one-handed melee weapon while using a shield in your other hand, you may take a -5 penalty to hit to add +10 to damage." Let's also ignore JC's terrible ruling on the Shield Master bonus action. Let's boost Str to 18, since he doesn't need PAM.
Assuming you shove prone for advantage, the spear damage is now 1d6+2+4+10 or 19.5 avg, and accuracy becomes 69.75%. (Was 65%, boosts to 70%, 70%-25% with advantage becomes 69.75%) So damage is now 2 x 0.6975 x 19.5 = 27.2 eDPR. It'll come down a bit because the shove has a variable success rate. Probably a little too good for a fighter, a GWM fighter does roughly equal damage since it doesn't have a reliable source of advantage.
I'd love to see another mechanic besides the -X/+X mechanic for damage boosts, if there is one.