To my mind that is a sensible way of working. I believe some directors behave like leaders. The crew follow their orders. Moreover, I think that therein lies the essential difference between a cineaste and a writer or painter. I usually tinker with the script on set.
Any film can have all sorts of problems and difficulties to overcome during production.
You often have to adapt to unforeseen situations. But the major modifications to the script come from the actors. The players have to feel comfortable with the dialogue and the action. The screenplay is something written. In performance, the actor can sometimes feel awkward or ill at ease.