While an appreciation of stylistic difference is often to some extent subjective, the variations within books such as these are wide enough to make it unlikely that a single author is responsible for all the material.
(John Barton, "Source Criticism (OT)," ABD 6:163.)Compare this with:
No definite evidence, however, can be drawn from differences of vocabulary and style, as any author is able to remold a written text (although not all NT writers do this), or, on the other hand, to adopt the style and vocabulary of a source in passages which he is going to write himself. Therefore, observations on different style and language can only have subsidiary importance.
(Dietrich-Alex Koch, "Source Criticism (NT)," ABD 6:166.)So stylistic differences are both crucial and largely meaningless for source criticism.