Except that an observer located in the (hypothetical/approximate) common reference frame, but situated halfway to Mars, will report observations inconsistent with this definition (NB of course we receive their report at a time consistent with the definition, but the contents of the report are not consistent). So yes, you can play games with your definition of simultaneity, but you will win stupid prizes like observers in the same reference frame no longer agreeing about simultaneity when such a result is worse than what relativity requires.

Your link points this out. You can play these games; I don't dispute it. But it's a separate matter entirely from anything to do with relativity, as your link points out, which is itself separate from the classical problem I originally posed. So we are now two steps removed from anything relevant to the Mars rover; I guess we get a sense of pride and accomplishment?