Here's what I'm not following: you're not explaining why it's not worth it. You're making an assertion, saying it's not worth it. You're saying other choices are better and claiming they're better because of action economy. But you're not explaining why.
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My point here is that most of the game is going to happen after level four. Which means the dual wielder is going to be able to take advantage of a lot of combinations when it comes to the special abilities of weapons.
I would argue that some of those combinations are already powerful at this stage of the game. The most powerful of which is the Xyanyde example above, in my opinion. But there are also combinations involving the Shattered Flail.
Mixing and matching the weapon choices is not only fun, it's potential for power in combat is undeniable.
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And what bonus action am I going to trade this for?
The chance to shove? My primary weapon already does that if I want it to. Or I could use a push martial ability while adding a d8 to my attack. So, no, shove isn't attractive enough to replace my offhand attack.
In other words, where's the action economy?
Are there times where I'm going to need to drink a potion instead of using an off hand attack? Sure, probably, though I would argue that those times would be rare. Especially if I have a cleric in the party for healing and buffing or if I'm wielding a weapon that actually heals or buffs me in addition to hurting the enemy.
Your DPS calculations are entirely missing the amount of other Bonus Actions used. They directly reduce the damage output. As pointed out, there are lots of good Bonus Actions in 5e, and MORE in BG3.
Your higher level logic is backwards as well. When you get extra main hand attacks, the single off-hand attack damage becomes less significant. Weapon properties work with the same logic, they are much more powerful as your main hand weapon if you have 3 attacks on that. There will eventually be Shields with properties as well for extra off-hand benefits without a fighting style and feat requirement.
And you're vastly underestimating the power of the empowered Shove that doesn't spend any resources and doesn't compete with a main hand attack.
