Uh what? If the request was appropriately formatted, not too large, and generally acceptable to the server from a transport perspective, why shouldn't it succeed with a 200?

Error handling is an application level concern, not a transport level concern.

HTTP status codes lack the nuance required to inform the end user about errors in any non-trivial application. I personally enjoy the OP's solution. I've worked on dozens of REST APIs in my life, and I always prefer those that contain a response envelope complete with metadata and error responses.

Pre-emptive edit: When I say error handling is an application level concern, I don't mean "application" from an OSI model perspective, which is narrower in scope than what I'm talking about.