Just want to quickly throw in a little bit of praise. We can at least toggle off auto-filling the hotbar in BG3. By default all the junk you pick up gets added, but if you deselect those settings in options then the hotbars get molested a lot less. It does mean you will have to configure them yourself, but a little micro beats never having a clue where various abilities are going to be.
But rather than having a gargantuan bar of everything, I think a slightly better option is having dedicated spaces for weapon configs, potions, spell and spell like hotkeys, and then a proper casting interface for better access to all the stuff that isn't in the quickbar.
The big problem with quickbars that contain everything is that they stop being quick. It's the difference between pulling something out of your pocket and pulling something out of a stuffed backpack. Unless you know *exactly* where your things are packed, it just isn't very easy to find what you're looking for in the backpack. But you'll only have one or two things in your pocket, so that process is always easy, precisely because it isn't cluttered all to hell and gone.