"Writing an essay is homework."
I think nearly all of the examples should have actually been のが . It's much more natural. のは is only really used when you are specifically comparing two sentences, and emphasising the current one. Confusing, I know.
「作文が宿題です」 should be accepted. The letter 作 means "compose" and 文 means "text, sentence, essay". Thus 作文 itself can mean "writing an essay". 「作文を書く」 is a duplication and sounds awkward. Reported on Oct. 30, 2017.
Is 作文を書く definitely wrong? We can say either "writing an essay is homework" or "an essay is homework" in English.
The English translation is strange. A teacher would say, "You must write an essay for homework" or "Tonight's homework is to write an essay."
The student might then say, "My homework is writing an essay/to write an essay." IDK, any thoughts?
I could understand: "Writing an essay is HARD work."
I think the purpose of the English translation is to keep approximately the same word order to show the connection between words. Though it might result in a slightly awkward sentence, it is grammatically correct.