Eliezer's "metaethics" sequence, despite its name, argues for his ethical theory
Yes; what else would you do in metaethics?
Isn't its job to point to ethical theories, while the job of ethics is to assume you have agreed on a theory (an often false assumption)?
Ethics is the subject in which you argue about which ethical theory is correct. In meta-ethics, you argue about how you would know if an ethical theory were correct, and/or what it would mean for an ethical theory to be correct, etc.
See here for a previous comment of mine on this.
There seems to be a widespread impression that the metaethics sequence was not very successful as an explanation of Eliezer Yudkowsky's views. It even says so on the wiki. And frankly, I'm puzzled by this... hence the "apparently" in this post's title. When I read the metaethics sequence, it seemed to make perfect sense to me. I can think of a couple things that may have made me different from the average OB/LW reader in this regard: