the Austere Metaethicist replies:

"Tell me what you mean by 'right', and I will tell you what is the right thing to do."

That is of course, not what is right, but what she thinks is right. So far, so subjective.

You may not know what you mean by 'right.' But let's not stop there. Here, let me come alongside you and help decode the cognitive algorithms that generated your question in the first place, and then we'll be able to answer your question. Then we can tell you what the right thing to do is.

Again, that is not the right thing, that is just what she thinks. An Objective metaethicist could answer the question what is right.

But moral terms and value terms are about what we want.

No: they are value terms about what we should want and be and do.

And the "we" is important here. Your metaethicists are like therapsists or life coaches or personal shoppers who advise people how to make their individual lives spiffier. But moral action is not solipsistic: moral choices affect other people. That's why we can't stop at "whatever you think is right is right". I don't want one of your metaethicists telling my neighbour how to be a better serial killer.