dual wielding changes in future dnd editions, but dual wielding 5e overall isnt that bad. It has strong interactions with multi attack buffs. It beats two handed weapons easily unless you have a great weapon master or sharpshooter build with high attack, or easy advantage
By "multi-attack buffs," do you mean effects that deal extra damage on each attack? These seem required to make dual wielding competitive on non-rogue characters.
It's important to keep in mind that in 5e D&D, not every class is meant to benefit from dual wielding. Only Rangers and Fighters get the two-weapon style to use it.
Even taking into account TWFS, dual-wielding still seems strictly worse for Fighters at level 5+.
- Level 2 Fighter with TWF shortswords: 0.65*2*(1d6+3) = 8.5 expected damage, at the cost of their bonus action
- Level 2 Fighter with GWF greatsword: 0.65*(2*4.167+3) = 7.4 expected damage (1d6, reroll 1 and 2, comes out to 4.167 damage)
- Level 5 Fighter with TWF shortswords: 0.65*3*(1d6+4) = 14.6 expected damage, at the cost of their bonus action
- Level 5 Fighter with GWF greatsword: 0.65*2*(2*4.167+4) = 16.0 expected damage
Already at level 5, with a single additional extra attack, 2H'ing a weapon beats out dual wielding. And you still have you bonus action available!
If you have +1d4 on each attack (dipping, magic weapon, etc)
- Level 5 Fighter with Dipped TWF shortswords: 0.65*3*(1d6+4+2.5) = 19.5 expected damage, at the cost of their bonus action
- Level 5 Fighter with Dipped GWF greatsword: 0.65*2*(2*4.167+4+2.5) = 19.3 expected damage
Dual wielding slightly beats out using a 2H weapon, but only if you use your bonus action making that off-hand attack each turn. Your dps plummets if you have to continually spend your BA doing something else (dipping on your first turn, Second Wind, BG3 homebrew BAs).
Rangers are more suited for two-weapon fighting I suppose, as they don't get Great Weapon Fighting Style or a 2nd Extra Attack at level 11, and they also get Hunter's Mark.
