Lots of companies outside the tech industry still have to recruit CS and other tech majors. The demand for specifically English majors outside tech doesn't come close to balancing things out.

Which industries hire for English majors? Are there good opportunities to be had, and are future prospects looking stable,upwards or down?

Industries where writing and reading comprehension arein demand, such as advertising, journalism, marketing, film, diplomacy, public relations, publishing, technical writing, law, and many more ...

For those fields, wouldn't one be significantly better of with a degree in advertising, journalism, marketing, film/media, policy (local/foreign), print/media, engineering, law?

That kind of education doesn't teach you to reason, to understand the world, and to think critically (except about a narrow subject). I'd much rather hire a liberal arts major - the vocational stuff can be learned later.