A failback placeholder is a 404…
5xx is a failure to serve the page, which is not the case if a placeholder is served
5xx is a failure to serve the page, which is not the case if a placeholder is served
5xx still returns content. 5xx can return HTML content. Browser will display it properly.
4xx codes mean client error. 5xx codes mean server error. Server misconfiguration is a server error. Client did nothing wrong.