My MC locks in conversation with a character. That character now faces away from his own goods, or a door he's supposed to be guarding or whatever. I switch to Astarion and sneak. Because said character locked in dialogue or combat or whatever is no longer facing in that certain direction...
This is something a lot of players really like. I'm sorry you don't enjoy it, but unfortunately changing it would disappoint others who do.
Some people screech about "bad design" like it's an engineered bridge that can't carry a load of cars and will inevitably collapse. But that's a fundamental misunderstanding based on a singular and narrow point of view. It's not how it works. The truth is: Some people like it. Some people don't. Everyone can't be pleased by everything.
It's not a broken design or a flaw. It's a feature of the game. Luckily, for players who don't like this feature, most of these examples can be avoided in play. For example, the game doesn't require anyone to talk to an NPC before sneaking. That's not a prerequisite of progressing the story.
Here's the thing about features though. If this is the game working as intended, then Larian is going to build the rest of the game with those features in mind. They're going to build the game with the knowledge that the players have these tools in their toolbelts. Why should we assume that at higher levels, difficulty isn't going to be balanced around various exploits? If these are meant to be there, then what logic would move Larian to ignore them when thinking about how difficult to make enemies? Why wouldn't they give enemies more health when they know that players can throw healing potions? Why wouldn't they think "hey there should be a sneak puzzle here," thus forcing players to engage in the exploitable stealth system? Why wouldn't they inflate the cost of things in shops to account for how easy it is to game the store system? Why would they create all these systems and then forget about them when designing the rest of the game?
