Forcing you to consume a bonus action for your off hand attack is a questionable design principle.
"Hey, I just had a great idea. Dual wielder, the offhand burns the bonus action, to get extra DPS! I coded it, done!"
"Sounds like a good plan, oh, I hear the ice cream truck bell. Let's go. I hope you remember to think this through later!"
It's not really about coding, it's about the D&D rules. Whereby, offhand attacks cost a bonus action.
The design principle being that Dual Wield gets easy access to weaponizing their bonus action because they can just slap enemies with their off-hand weapon (Even better with TWF for stat modifier as damage).
While 2H weapons instead have to jump through hoops to utilize their bonus actions for damage (Polearm Mastery, Great Weapon Mastery, Frenzied Strike etc)
1h + Shield forgoes the ability to weaponize their bonus action in favour of the AC bonuses from having a shield.
With 1h only (Ideal for any Duelist or Swashbuckler themes) being gimped forever and never supported in any way, shape or form at all outside
maybe some specific magical items (BG3 has the Gloves of the Duelist for +2 on attack rolls and Duelist's Perogative Legendary rapier)
In other versions of D&D there have been times when dual wielding has been so much better than other options too. Either from lack of ways for 2h to use bonus actions, to 3.5e's Tactic Feats (Namely the one where if you get a Crit then a nearby ally with the same Feat will do a free Attack of Opportunity against the target too. So more attacks = More chances to crit = More free AoO's from allies during your turn)
The only real "Janky code" is BG3 trying to give a QoL feature to players so they can do both attacks with a single click/button press. With this QoL feature not factoring in times when the main-hand attack already kills a target (So will still consume that off-hand attack on a dead target)
Now you have to play all kinds of silly games to get extra bonus actions, a Frankenstein build that has little to do with the concept of a traditional dual-wield fighter.
Technically, that's a BG3 problem, not a design problem. BG3 homebrewed the Fast Hands ability to give an extra bonus action. In actual 5e, there isn't such a bonus on ANY class. So at worst you just need 1 level of Fighter or 2 levels of Ranger for TWF. Even this is specific to 5e too, prior editions had alternatives (I.e. In 3.5e Rogues got the ability to make specific weapons (What we now know as Finesse weapons) utilize their Dex modifier for attack and damage regardless of which hand it was in)
Meanwhile, nothing from a video game will even approach the actual concept of a traditional dual wield fighter. In which the off-hand weapon is literally just a bad shield that will
occasionally be useful to stab someone after a main hand parry.
The notion of a "Dual wield fighter" who actually goes about swinging 2 weapons around is pure fiction. With dual wielding in real life consisting almost entirely of an off-hand dagger to use for parrying (With the only notably prominent style was for dueling with Rapier and Dagger) with it not being overly popular due to the terrible nature of how a dagger performs defensively compared to even a tiny buckler (Low mass of the dagger means it is very easy to displace with any other weapon. In addition, your hand is more exposed and can be sniped by quick cuts compared to a buckler)
