I can't agree with multiplayer hurting the single player experience - how does it do that?
It's not even a matter of agreeing or not, it's pretty an much objective statement that keeping that door open for multiplayer capabilities is limiting/affecting the design in plenty of ways even for people who aren't interested in it.
Aside for the good old and universal "Allocation of resources" you have the developers themselves admitting that the current "lack of passing time" and absence of a day/night cycle were decided according to the idea by the idea that it "would get messy in multiplayer". Now, in all fairness in this case it's mostly Larian designers lacking imagination and ambition, because if they really tried the workaround around this issue was absolutely possible, but still... "Word of god", as they say in these cases.
The fact that characters need to have their distinct inventory window, despise the fact that items can be used by everyone regardless of which inventory they are occupying in single player? A byproduct of multiplayer. The fact that the game refuses to default dialogue to a single leader? A multiplayer byproduct, too. The way multiple characters are written to be "main character" concurrently? Another multiplayer byproduct.
And to be clear, you may love multiplayer and think that this is absolutely a feature worth all the downsides. It would be a perfectly legitimate opinion, as far as I'm concerned. But you simply can't deny that co-op being a focus in design is affecting the game even for people who don't plan to make any use any of it.
Party control in Baldur's Gate 3 is a complete mess that begs to be addressed. SAY NO TO THE TOILET CHAIN