the core of BG3 is basically DoS2. Must be trouble to change the code, who knows. Do they even care? Who knows.
After three games I assume there is something they get out of it that they want to keep.
Perhaps there is substantial amount of players not familiar with multi-unit control, and find it easier to engage with this single character control, other follow? Whatever the reason, surely they can make chaining characters swifter and more reliable then it is.
