Dual wield do more reliable damage but actually cost both action+bonus.
2H weapons look to be dippable as well iirc ?
I'm also not sure that off-hand wepon will stay like this (it is meant to not have bonus to hit or damage without feat), so probably will be, on average, less efficient per action.
Heavy 2H weaponry on a fighter taking the great weapon mastery can deal far more damage per hit but need advantage to be reliable (and a blessing too).
But with proper feats/spells/classes (mark of the hunter, hex, sneak attack for instance), hitting two times may be far more efficient since bonuses are added for each roll (and have chance to both crit, multiplying all added bonus dice).
With no special abilities to those, you'll have either :
- shortsword (1d6) + dagger (1d4) + 1x proficiency + 2d4 fire (if dipped) = 4-18 dmg + modifier if both attacks hit.
- Greatsword (2d6) + 1x proficiency to rolls + 1d4 fire (if dipped) = 3-16 dmg + modifier with one attack to land.
With one dice bonus (sneak attack of mark of the hunter) :
- shortsword (1d6) + dagger (1d4) + 1x proficiency + 2d4 fire (if dipped) + 1d6/attack = 6-30 dmg + modifier if both attacks hit.
- Greatsword (2d6) + 1x proficiency to rolls + 1d4 fire (if dipped) + 1d6 = 4-22 dmg + modifier with one attack to land.
With Dual Wield feat / Great Weapon Mastery :
- shortsword (1d6) + dagger (1d4) + 2x proficiency + 2d4 fire (if dipped) = 4-18 dmg + 2x modifiers if both attacks hit.
- Greatsword (2d6) + 1x proficiency to rolls + 1d4 fire (if dipped) + 10 = 13-26 dmg + modifier with one attack to land, but with a -5 to hit.
It more of a matter of playstyle and feats available to your class than one fighting style being superior to another.
Dual-wielding makes you more polyvalent since you can split damage on two targets
