I find this an odd conversation. A two handed weapon for a barb deals 2d6+STR+2. Dual wielding deals 2d6+STR+4. Dual wielding requires an extra action that you miss out on the round that you rage. Two handed weapons means you don't have to roll to hit a second time, but on the other hand you also don't have a second chance to hit. Against AC 10, the damage output is basically comparable and the higher the enemy AC goes the more attractive dual wielding gets.
Rogues won't always want to use cunning action. Dual wielding gives you 2d6+DEX+Sneak attack. One handed gives you 1d8+DEX+Sneak attack. If you don't end up using your offhand weapon because there is a better use for your bonus action, that's an average difference of 1 point of damage and one handed will only deliver better damage than dual wielding about a third of the time against AC 10, and again the higher the enemy AC goes the more attractive that second attack becomes.
Plus you can keep rage going while using your standard action for something else.
You get attacks with BOTH weapons for opportunity attacks.
You can trigger additional advantageous effects on your weapons.
If you can find magical offhand weapons, the effectiveness of dual wielding only increases.
It's a perfectly viable, even appealing, system.
Sometimes there will be a bridge to shove somebody off of. There are a LOT of situations where that is not the case. You will only occasionally give up the extra damage from your offhand weapon to shove, and then mostly because shoving was the best thing to do anyway so the main attack was just extra.
Honestly it doesn't remotely bother me that shoving is the best strategy when you are running around the rafters or catwalks over lava. It SHOULD be the best tactic in those situations!
And if you are going out of your way to create situations where you can shove people off ledges, then that has nothing to do with dual wielding or wielding anything at all. But just because that is the tactic you've chosen to embrace does not mean it's the best one.
That said I have been playing with the shove and sneak as standard action mods for a long time now and I do think they make the game better, mostly because all of the shoving makes fights look like an episode of the three stooges. But the notion that shoving makes dual wielding ineffective is just ludicrous.
Dual Wielding isnt really an issue with BG3, its a system issue. Its just that most classes need their bonus actions, and that Dual Wielding takes a bonus action. As you also said, you get limited to 1d4 to 1d6 weapons without the Two Weapon fighting style and the Dual Wielding feat, which let you dual wield up to 1d8 weapons (Rapiers for Dex, several options for Str). There are classes like Barbarian that, depending on subclass, could either wield a two handed weapon and use bonus actions for other things, or dont use their bonus action and may want to wield dual 1d8 weapons. The issue really comes down to is there is just too many free bonus actions in the game that it truly shows the issue of Dual Wielding in the 5e system. Why waste a fighting style and a feat when you can take a better fighting style and an ASI/better feat at level 4. It all comes down to that action economy and what you want to spend those actions on, and sadly some options are just not worth it.
