Just to be clear...
In film, the screenwriter is the STORY TELLER - as the playwright is in theatre. The film director (working with the editor – and editing absolutely crucial to the audience’ experience) is the STORY REALISER.
Understanding these roles begs the question: why do so many film directors get involved in the story telling side of film making, aka screenwriting? By and large, theatre directors don’t get involved in the creation of the stage play script; so why do film directors get involved in the development of the screenplay of the film they want to make? This suggests they don’t trust the screenwriter to do their job properly, and that the director knows more about screenwriting than the screenwriter. If that’s the case, fire the screenwriter and find on who knows what they are doing. But how? If you don’t know a good screenplay from a doughnut, how can you recognise the quality of one film script over another?