You demand that everyone accept your definition of ethics, excluding moral luck from the subject, but you simultaneously demand that meta-ethics be defined by convention.
I said both of those points (but not their conjunction) in my previous comment, after explicitly anticipating what you say here and I'm rather annoyed that you ignored it. I guess the lesson is to say as little as possible.
Now just hold on a second. You are arguing by uncharitable formulation, implying that there is tension between two claims when, logically, there is none. (Forgive me for not assuming you were doing that, and thereby, according to you, "ignoring" your previous comment.) There is nothing contradictory about holding that (1) ethical theories that include moral luck are wrong; and (2) utilitarianism is an ethical theory and not a meta-ethical theory.
(1) is an ethical claim. (2) is the conjunction of a meta-ethical claim ("utilitarianism is an ...
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: