In my experience (especially with Elsevier), their copy editors are doing more harm than good. I dread having to go through proofs, as they always manage to sneak in mistakes, from spelling errors to changes in equations or figures.

My advice to students: NEVER just accept the proofs they send you, ALWAYS do meticulous proofreading of the proofs even if your manuscript was flawless. I'm aware of one case where they removed the entire abstract, and since the authors didn't notice that when checking the proofs in the publisher's online proof-checking system, the paper was published that way. They had to publish an erratum with the abstract because, once published, they don't allow changes to articles, even if it was clearly a mistake by the journal. (Disclaimer: It wasn't my paper, so I don't have an axe to grind here; I just found it appalling.)

I've given up checking the manuscript proofs, it's a waste of time. The real paper as it was intended is available on arXiv.

Yes "editors", those are people who will write you back "article does not conform with spec"(honestly though I think that's just a bot using their emails) until you fix the formatting yourself. And will send you the joined replies from the per reviewers.

They are not editors in any real sense of the word.

I do not think they are bots. A bot would not ask you to submit an appendix as a separate file in the first submission and merge it after the first review, for example.

Most of the work they do is, indeed, forwarding emails (not even reading reviews and authors responses). However, from time to time, they have to solve difficult issues (corrections, conflicts, plagiarism) and for that you need a person.

Yes.

Examples:

https://journals.aps.org/departments/editorial.html

https://www.nature.com/nature/about/editors

The list of Editors, Senior Assistant Editors, Assistant Editors, Assistant Senior Editors, Executive Editors, Editors Adjutant, Editors Emeritus, and Editors-at-large _did not stop scrolling_!

I have found that copy editors and layout people add an immense of value to the final product.