Should the PhD proposal be discussed and adjusted by supervisor and student before formal application?
You will probably join an existing work group, and work on the projects of the advisors. You will get some job that (somewhat) aligns with your interests (and competence), as asking for stuff you don't like and aren't competent in is just wasting a (valuable) position. Other than that, your thesis will be directed by their pressing interests, not yours. Laying out a detailed proposal as first contact is just a waste of everybody's time. You will work it out with them, eventually.