One concern I have is the saying that "weapon damage dice don't kill monsters, bonuses do". (Okay, that saying was from AD&D 2ed, and probably just one DM, but still.)
The base case works fine. But can this be abused?
A couple of things I can see:
A single level fighter dip can double a rogue's chances to land their sneak attack without taking up a second hand or using a bonus action (which has a good amount of competition for the rogue). And it's higher expected damage than TWF since the second one gets that ability score added to damage, even though is is superior to it except for weapon die size, and since TWF is restricted to light it's not far behind it.
A different way is if you start piling on bonuses, does it exceed? Barbarian rage bonus damage, a second fighting style to take dueling as well, just getting an extra use per round of a magic weapon. Something like the Holy Weapon spell from XGtE, or Hex / Hunter's Mark?
Hmm a Ranger 4/Fighter 1 with Swift Striker, Dueling Style, and Hunter's mark gets two attacks for d4+(STR|DEX)+2+d6 = average 8+S|D per hit, or 16 if all hit. A fighter 5 with traditional Dueling style would have 2 attacks with d8+(STR|DEX)+2 = average 6.5 per hit or 13 if all hit. But then at the next level the Swift Striker, which is already doing more damage, would get a third attack and blow other out of the water. (This doesn't require multiclassing, the Champion gains a 2nd fighting style natural, though it comes online later.)
This looks like those looking to optimize can squeeze a lot more out of it than an average users. That's might be something fine for a particular table though.