I believe that Larian has some emotional attachment to this system. It looks like something you created and deeply believe is good, but everyone says it isn't. And although it isn't a terrible solution, the chain/unchain system is no better than the classic mode (BG1, BG2, Pillars of Eternity, Pathfinder Kingmaker...).
So, Larian needs to give this up and implement a better system (the classic) in which you simply click on someone you want to control or draw a square on the screen to select more than one character. Or select one of them, hold Shift and select the others (Backspace to select the entire group).
Perhaps they can adopt a mix of these two systems where if you select more than one character, it will show a lock for you to "link" the characters together.
And the game really needs Formation Options because it's frustrating to see your group taking strange positions on the battlefield before each fight.