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 .8Polearms = E[1d10|GWF]= (5.5+5.5+3+4+5+6+7+8+9+10)/10 = 63/10 = 6.3, a
gain of .8Greatclub = 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?
Best Answer
This change is unbalancing as it makes the Dueling Fighting Style often strictly better than the Great Weapon Fighting Style
Let's look at the Dueling Fighting Style (D-FS), it states:
This is quite clearly meant to benefit those who wield a single one-handed weapon. The other hand could hold a shield, some item such as alchemist's fire or, in the case of a Swords Bard, Paladin, or Ranger, even be free to use a component pouch.
Also of note is just how much this increases your damage by; increasing the damage die size increases a weapon's average damage by 1. As such, increasing the damage flatly by 2 is similar to increasing the damage die size twice. This means 1d8 versatile weapons would be similar to 1d12 weapons (an average damage of 6.5) and 1d10 versatile weapons would be similar to 1d14 weapons (an average damage of 7.5).
Let's compare this damage increase to that of the Great Weapon Fighting Fighting Style (GWF-FS) which states:
GWF-FS, as discussed in the question "How much damage does Great Weapon Fighting add on average?, increases your average damage by (X-2)/X where X is the size of your weapon's damage die. Note, this number is always less than one, and so it is always worse than just increasing the die size once, let alone twice.
This change to D-FS would make it strictly better than GWF-FS in all cases except the 2d6 greatsword. Additionally D-FS comes with versatility of allowing the character to take up a shield (or other non-weapon) and still gain the benefits of the Style which is not the case with GWF-FS.
Below is a chart showing these differences, note that D-FS stops increasing after 7.5 because this is the maximum average damage when using this feature (when using a 1d10 versatile weapon).
Note: The "Difference" column is D-FS's average damage minus GWM-FS's average damage, so if it is positive then D-FS is the strictly better option.
\begin{array}{|lcccc|} \hline \text{Die} & \text{Average} & \text{GWF-FS Average} & \text{D-FS Average} & \text{Difference} \\ \hline \text{d8} & 4.5 & 5.25 & 6.5 & 1.25 \\ \hline \text{d10} & 5.5 & 6.30 & 7.5 & 1.2 \\ \hline \text{d12} & 6.5 & 7.33\bar{3} & 7.5 & 0.166\bar{6} \\ \hline \text{2d6} & 7.0 & 8.33\bar{3} & 7.5 & -0.833\bar{3} \\ \hline \end{array}
As you can see D-FS is better than GWF-FS in all cases except the 2d6 greatsword. This is clearly a bad move, as it completely overshadows the other Style.
Here is a chart showing what would happen if you restricted your D-FS change only to 1d8 versatile weapons (the D-FS's average damage would now max out at 6.5, when you are using a 1d8 versatile weapon):
\begin{array}{|lcccc|} \hline \text{Die} & \text{Average} & \text{GWFS Average} & \text{D-FS Average} & \text{Difference} \\ \hline \text{d8} & 4.5 & 5.25 & 6.5 & 1.25 \\ \hline \text{d10} & 5.5 & 6.30 & 6.5 & 0.2 \\ \hline \text{d12} & 6.5 & 7.33\bar{3} & 6.5 & -0.833\bar{3} \\ \hline \text{2d6} & 7.0 & 8.33\bar{3} & 6.5 & -1.833\bar{3} \\ \hline \end{array}
This makes the Style slightly better, allowing it to apply to the Quarterstaff, Spear, and Trident while they are two-handed. D-FS already can be applied to one-handed 1d8 weapons, so applying it to a two-handed quarterstaff won't increase the power outside of a Monk multi-class; however, the spear and trident can both be thrown so the Style gains some additional power as you now have a choice between a 1d8 weapon or a thrown 1d6 weapon.
Normally a character could wield a 1d8 one-handed weapon and a 1d6 thrown weapon, and to get a free hand, they would have to either drop a weapon (which can possibly go poorly if it is kicked away or stolen) or put the weapon away (which takes an object interaction).
With this change a character could go from wielding a 1d8 D-FS versatile weapon to having a free hand and a 1d6 thrown weapon with no cost to their action economy.
This is an incredibly specific/niche use though so I don't see it having much of an effect on gameplay. (It requires a character to want both a thrown weapon and a melee weapon out, and for some reason now need a free hand, and their object interaction; this seems like a niche enough case to me).
D-FS (even unchanged) is better than GWF-FS unless a character is specifically using a 1d12 weapon or the 2d6 greatsword. The difference in the average damage between 1d8 D-FS weapons and 1d10 GWF-FS weapons is only 0.8333.
I personally do not feel that this is enough of a difference to warrant taking GWF-FS given D-FS's greater versatility in allowing you to take up a shield (or other non-weapon).
As a result the GWF-FS (unmodified) is restricted to the 2d6 greatsword, characters who will not use a shield (such as Barbarians), or classes such as Barbarian or the Champion Fighter and possibly Paladin, where critical hits are more favorable or more likely than usual (crits roll more dice, so for them, the rerolls from GWM-FS are better than the flat +2 from D-FS). This is already a thing, and the modification to your change suggested here doesn't make that gap any worse.
Making your change in general makes the Great Weapon Fighting Style strictly worse unless you are using a greatsword.
Making your change only apply to two-handed versatile 1d8 weapons is quite reasonable as the feat already applies to one-handed 1d8 weapons.