I am honestly surprised over the name “Dark Ages”, because this has such a negative ring to it. And the lack of cultural production seems a little too harsh, as well. I would say that you can see how cultures are been borrowed, and are influencing each other. Just look at the Byzantine earrings that Queen Arnegunde. Now, if it was friendly “sharing” of culture, or if it was impacts from wars and pillaging, I don’t know. But there is a spread of cultures.
The artwork seen from the Vikings, the Norse, and the Celts, does not look like it came from a dark age or any age that was inhibited of cultural production and innovation. If we look at the books and gospels, these are bright and intricately decorated, they have a bright and positive tone rather than dark. The intricate designs that we see, where there is braided and winding branches and patterns is gorgeous and very innovative.
In short, the “Dark Ages” is a misconception of this era. There was plenty of innovation and cultural production that we can see reflected in the art.