As a DM, would allowing players using a versatile weapon in two hands to benefit from Dueling create unforeseen imbalance in the game? The reason for this change is because it appears that the longsword, when used without a shield, is far outmatched by the greatsword in terms of damage. Whilst the longsword has the ability to be used when grappling, this is not a significant enough advantage as a character could simply drop their greatsword (which would be a non-action) and use their object interaction to draw a onehanded weapon, like a rapier.
Whilst Jeremy Crawford’s unofficial ruling was that versatile weapons only benefited from Dueling if wielded in one hand, I disagree with this ruling. From a thematical stand point, it does not make sense that I would be more effective at using a weapon designed for two hands, such as a longsword, one-handed. From a mechanical stand point, allowing this only seems to make otherwise sub-par options slightly better.
From this post from a few years ago that compared the damage values of various weapons:
Average weapon damage:
EX: E[1d6] = (1 + 2 + 3 + 4 + 5 + 6)/6 = 21/6 = 7/2 = 3.5 or
(1/2)*[6+1] = 3.5
Greatsword & Maul: E[2d6] = 3.5 + 3.5 = 7
Greataxe = E[1d12] = 6.5
Glaive, Pike & Halberd = E[1d10] = 5.5
Greatclub = E[1d8] = 4.5
Averages with Great Weapon Fighting:
E[1d6|GWF] = (3.5+3.5+3+4+5+6)/6 = 25/6 = 4.2, so:
Greatsword & Maul = E[2d6|GWF]= 4.2 + 4.2 = 8.4, gain of 1.4
Greataxe = E[1d12|GWF]= (6.5+6.5+3+4+5+6+7+8+9+10+11+12)/12 = 88/12 = 7.3, gain of .8
Polearms = E[1d10|GWF]= (5.5+5.5+3+4+5+6+7+8+9+10)/10 = 63/10 = 6.3, a gain of .8
Greatclub = E[1d8|GWF]=(4.5+4.5+3+4+5+6+7+8)/8 = 42/8 = 5.3, a gain of .8
A longsword, having a damage die of 1d10, would therefore do 5.5 average damage and 6.3 if used with Great Weapon Fighting with a max damage of 10. If compared with using a greatsword, which has an average of 7 damage and 8.33 damage with Great Weapon Fighting with a max damage of 12, it is fairly clear which weapon is better in terms of damage.
However, if instead we compare a longsword wielded in two hands which benefits from Dueling to a greatsword, we get 7.5 average damage (5.5 +2 from Dueling) vs 7, or 8.3 if the greatsword is benefiting from Great Weapon Fighting. These numbers are significantly closer together, making longswords and other versatile weapons more viable options. Even spears and quarterstaffs become more viable options as their average damage increases from 5.3 with GWF to 6.5 with Dueling.
Considering that only Fighters, Paladins and Rangers can take Dueling, it does not unbalance the game in terms of giving everyone a damage boost. Additionally, none of the new damage increases outshine the greatsword as it still has a minimum of 2 damage and 12 max damage, 2 points higher than any versatile martial weapon or 4 points higher than a versatile simple weapon. Furthermore, versatile weapons would still not benefit from Great Weapon Master’s second benefit, meaning weapon’s like the greatsword could still outperform versatile weapons massively.
Note that a champion fighter could take both Dueling and GWF, benefiting from both fighting styles simultaneously, but even then a longsword only deals 8.3 average damage, comparable to the greatsword’s 8.33, but this requires the fighter to forego the +1 AC from Defense and requires them to be at least 10th level. Finally, as stated previously, versatile weapons would not benefit from GWM’s second feature so, by choosing to use a longsword instead of a greatsword, they are losing a further +10 potential damage.
However, whilst this all seems very balanced to me, what I want to know is are there any potential interactions which would make this change to Dueling unbalanced?