Maybe the director finds texts that don't match his or her conception of the work. Unless you already know the play well, you can never be sure of what has been added or subtracted. Obviously someone has to be in charge of the production and pull it all together. But because you can't see precisely what the director has done, you may credit or blame the actors or the writer when in fact a great director can make a bad play look good and a weak director can make a great play look bad. As the person most responsible for the overall sense of the play, the director is always deciding about how to follow the writers' intentions.
Personal interpretations are inevitable.
A lot remains for the director and the actors. Of such tiny details in one tiny moment the director shapes the final result into what ideally becomes a unified whole. Even if you can't be certain what the director has done, you can certainly discern a lot from the dialogue and how it defines character and motivations. You will be able to see whether the sense of the entire play holds together. If you witness bad acting, you know the director didn't correct it, even if you don't know why.