I think having a standardized currency has kind of become the norm on most "mainstream" CRPG these days - it's not just a Larian thing. In general most devs just don't think having a very complex monetary system adds much. Most of the big games use a single practical currency, and in most cases, any other are strictly added in others for world building loot.
For example - in Obsidian games like Deadfire or FNV - you often get to pick up other currencies as a world building mechanic (i.e. NCR dollars, Azata shells), but the underlying barter system still operates on 1 currency. In Deadfire's case everything just gets auto converted to CP. In FNV's case, other currencies basically operate like gems and other sellable loot, with bottlecaps being the main.
Alternatively, in Dragon Age origins, gold/silver/copper exist, but your money is automatically converted. I.e. if you pick up enough copper, you'll automatically get silvers.
In regards to the economy, I wouldn't mind seeing Larian try to tone down the economy a bit, but at the same time, it's sort inevitable when you allow for certain player freedom and save scumming that things can get out of hand. As long as your game is designed for both extremes (i.e. non-looters and Scrooge McDuck players), some form of exploit will exist. No amount of currency control can deal with players willing to spend time farming and save scumming to accumulating wealth.
In general, almost any game that has pretty open exploration and allow you to kill and steal from NPCs (with save scumming) will have some form of economy problem where players can get incredibly rich. Deadfire, FNV, BG1/2EE all have this problem similar to BG3. Games that tend to restrict freedom more (i.e. Kingmaker/WoTR - where you can't actually steal or harm randoms) can better keep their economy in check, but that leads to you outright denying certain playstyles.
In BG3's case, I wouldn't mind if some of the more obviously sellable loot is reduced in value (i.e. all those crystals you can mine). But if someone's really looking to cheese the economy of the game, I don't think you can really stop them without putting in too much restriction that affects QoL.
