And San Vitale in Ravenna, completed in 547, with its magnificent mosaics of Justinian and his court--obviously commissioned and executed after Belisarius's seizure of the city from the Ostrogoths in 540? Or also in Ravenna, San Apollinaire in Classe, begun in 535 and completed in 549?
Sorry, it doesn't cut it. There was a plague, bad harvest, external troubles, but there wasn't a "Dark Age" with loss of classical learning or a collapse of social structures in the Empire. And yes, everything did revolve around Constantinople, "The City": it was the Imperial capital from 330 on, and its European environs, together with Asia Minor has most of the population and wealth of the Empire.
I think we need a radiocarbon date here, but notice that what we have is an indefinite "end time". Might I suggest 538 was a good day to die, so to speak, and it's not excluded by the San Vitale documentation. I'd suggest radiocarbon dating for many of the other references you give.
Part of the difficulty is in finding independent documentation for any of the items you cite. For the most part, since this was a Dark Age, records simply do not exist, and those which do leave questions, particularly regarding dating.
We also have a problem with people who wish to believe that "barbarian invasions" brought about the Dark Ages.
Given the climatic devastation in Europe, it's more likely the "invasions" were simply groups of refugees.