That might be true some of the time, but we have items that give extra bonus actions and such, making dual wielding scale very well.
3d6 + 15 + 3d6 round 1
4d6 + 20 + 4d6 round 2
Only two items so far I can recall, both of which are conditional about how they grant that extra BA. One you have to be at 50% health and the other you have to use a fire spell so not ideal for a ranger anyway. I guess if you have a high elf cantrip? But then you are sacrificing your main hand for a firebolt that scales off of what's likely your dump stat (int). So the situations you would get these extra bonus actions are rare. Not really ideal items to build a ranger around. Meanwhile at level 5 without them, you will ideally be making 2 main hand weapon attacks to every one off hand attack (assuming you didn't have to hunters mark and can even use it). Seems better to add the +2 from dueling to that main hand that you consistently hit with instead of the +2 going to the offhand with two weapon fighting which isn't attacking consistently because of hunters mark application/jump/shove/etc. Plus being able to carry a shield boosts AC. You can also use a weapon that isn't light for a 1d8 (rapier) instead of a 1d6 (scimitar) Add in a potion of speed or a haste spell, both of which are easily acquired, and you can get four main hand attacks to only one off-hand (haste grants an additional action no bonus actions).
Personally, I think because of how reliant on bonus actions dual wielding is, it's best left to rogues, thieves especially. They might not get the fighting style like martial classes, but they can consistently get in an off hand attack every turn while still being able to do something else (potion/shove/jump/etc), or make two off-hand attacks for every one main hand attack. Certainly not saying dual wielding ranger isn't viable if you want to do it for fun, but it's a poor fighting style choice compared to the others mechanically speaking. Hopefully they adjust this a bit before release. If you could consistently land the off-hand it would probably be the dominant fighting style for rangers (assuming hunters mark) and more viable on other marital classes. Till then I would advise people to pick dueling, archery, or defense over it.
Funnily enough, a Hunter Ranger with Colossus Slayer and dual wielding is capable of meeting Blastlock Baseline for lvl 2, 3 and 5 without spells, even beating it with a good margin. So the damage is high enough to justify the additonal ranged abilities and spellcasting, though it tends to fall off at higher levels and with specific feats. BG3 seems to be including a lot of additional accuracy boosting things to make Great Weapon Master absolutely broken, so that won't be fun to deal with the fallout off, balance wise.
Larian also completely screwed the pooch on their handling of bonus actions. Shove and hide for everyone on BA? That is horrible. Shove is supposed to be an attack action and only Rogues should be able to hide on BA.
Then again, it's not like tabletop isn't problematic with its balance. There are basically 3 martial builds that work for optimalization.
Polearm Master + Sentinel + Great Weapon Master with a halberd / glaive for a strength based frontliner, can be put on any class with medium or heavy armor, martial weapon proficiecny and extra attack. Paladin 6 -> Sorcerer is probably the overall strongest option here. Other good options are Totem Warriors, Hexblades, Gloom Stalkers and even Valor Bards for their additional spellcasting.
Archery Style + Crossbow Expert + Sharpshooter for a ranged build. Gloom Stalker 5 - Arcane Trickster version of this is one of the most BS characters I've had to DM for.
And Ranger or Fighter 5 -> Rogue for a two weapon fighting dex build that balances ranged and melee combat. Why twf instead of dueling? Increased effective Sneak Attack accuracy, which you need to scale the damage to higher levels. It doesn't have the extreme highs of GWM or Sharpshooter when party support kicks in, but it is a bit more independent, making it less dependent on casters, who often have more important things to do than keep Bless up at all times.
If we're getting multiclassing for BG3 I can imagine that a Hunter 5 -> Thief will be quite insane as a dual wielder, with 2 BAs and two weapon style. Add the helmet for an additional BA, then add the Sneak Attack dmg and it should be pretty insane.
