This was one of my main issues, I have no idea how or why this design was settled on, but making it awkward to simply move individual members of the party is...bizarre.
I can only assume it started as technical limitation that a smaller indie game like DoS1 didn't have the resources to solve. Larian needs to solve it now though; they're out there saying BG3 is a AAA game, and no self respecting AAA game would leave such an important part of its design so much worse than the genre's decades old standard.
Just wanted to add that I agree 100%
The chain/unchain system is simply unacceptable on an AAA game and a sequel to a game that did not have this issue - it doesn't add any benefits to party control, and all of it issues as exacerbated by a combination of derpy pathfinding, and no fast and easy way to pause (entering turnbase mode is clunky and terrible).
I can't recall how many times I wanted my party to just stop right where they are and simply can't - and the rest of the party proceeds to circle and dance around the controlled character to flash mob their way into formation.
In a game where terrain has gameplay effects and traps are set by stepping over them, it's a terrible design.