Historians really don't debate the dark ages anymore. That term has been out of favor for a while. Only folks that seem to perpetuate that the myth of a "dark age" is Hollywood.
The period is already typically divided up into Early, High, and Late Middle Ages. There was a lot going on and in Europe it was an especially tumultuous time. Germanic Migration period was between 500 and 700. Slavic migrations around the same time. Merovingian period probably 480 to 774? Carolingian period was really only 775 to 900. The Viking age was 792 to 1066. Byzantine Empire was at it's high point. The rise of Islam. Rurikid Dynasty sprung up in Kiev and Novgorod around 800. Crusades, end of migrations, consolidations of what would become modern states. It's a bit difficult to pack all this into 500-1000 was X and 1000-1500 was Y.