Calling the Roman Empire 'daqin' meaning "Great Qin (China)" is a fairly meaningless appellation. What is "Great China" or "Great Qin" if you didn't know they were referring to the Romans?
By the apparent nonsensical names they gave to the states in the west. That is if we are going by your linguistic reconstruction, which overrides the actual pattern in the naming that give them meaning and significance. Regardless, this is off topic. I only brought it up because of your initial hostile response.
Again, maybe some other time I can show you that Guanhua probably underwent very little changes and that there is a problem with your conclusion.