If I'm correct the description for Dueling mentions that the other hand needs to be empty, so no shield!
You're right, Larian's description is changed from table-top (where it's clearly worded to be okay with shields), and does state "empty hand", but it is not currently implemented as such.
In game,
dueling works with shields, which follows the
5e Table Top ruling.
I agree the +1 AC would be too much. I had forgotten the Defense class passive already gives +1 (and not +2 like I thought).
I'm thinking Dueling is maybe more (only?) interesting for Dexterity characters, who will use a rapier.
With a great weapon, the character has either 2d6 damage (7) or 1d12 damage (6.5). Plus can reroll 1s and 2s with the class passive.
With Dueling, and a one handed weapon, the character has 1d8 (4.5) +2 = 6.5 damage. The good thing is that the minimum damage becomes 3 (and not 2 or 1 like with a great weapon). I'm not 100% sure about the maths here, but I would still pick the Great Weapon Fighting class passive over Dueling, unless playing a Dexterity character.
Dueling does sound like a thematic choice for DEX characters. Mechanically though, as long as Dueling works with shields (minimum +2AC) like in Table Top, it's often the better choice from a pure min/max perspective.
If we're only looking at damage, I also actually prefer the +2 from dueling.
Damage boosts only have a tangible effect when it changes the # of hits you need to kill an enemy.
The flat +2 (44% increase to 1d8 avg (4.5)) is much more likely going to change that for you than the Re-roll 1s/2s - (average 19% increase on 2d6 avg (7) - which is the optimal weapon for GWF).
You have to remember that GWF doesn't trigger on 3s or higher (which is terrible on 1d10 Polearms and 1d12 Greataxes), and when you get to re-roll, you don't even get to take the better of the 2 rolls.
