Creation(Playwright) is not synonymus with interpretation(Director)
Composer - Conductor
Playwright - Director
The conductor has interpretive control, and even has rights to recordings of his/her performances...but has not rights to the notes on the page and any honest comparison to their production choices to another conductors is subjective at best.Aside from blocking...to my mind this situation sets a precedent that playwright/director situation can emulate.
If a director steals, then it is from another director. Therefore, the director has the right to attempt to sue the other director, but not the playwright, the producing organization, or any other body.
The Conductor has more in common with most theatrical directors than a theatrical director has with a film director.
Although highly valuable, the theatrical director's contributions to the event are subjective. Therefore, aside from blocking, there is no way to objectively judge whether or not one director has stolen from another, such is the fate of an interpretive artist versus a creative artist.
The only measurable contribution a director makes is blocking, everything else while valuable is ultimately unverifible, ethereal and therefore unfit for copyright. I thinks director of a world premiere could ask for a cut of royalties for a specific amount of time, the same way a producing organization does.