History. Philosophy. Psychology. Linguistics.
Note that I don’t list English. The best understanding of people and behaviour and the workings of language come from those four. English serves its purpose – not always the purpose of a writer. Anyone serious about writing should already know how to read text carefully upon entering post-secondary education.
English, as a discipline, can expose wonderful concepts and introduce exceptional mentors but is not unique in this. It can deepen understanding of the world through narrative but relies on those four core courses for that narrative. It’s not that English should be ignored. Only that it should not be viewed as a prerequisite for successful writing. The danger in pursuing English to become a writer is the danger of fiction eating itself.