What place did Byzantium occupy in the world at the beginning of the Middle Ages?

What place did Byzantium occupy in the world at the beginning of the Middle Ages? Were the assessments of the modern people who considered Constontenople the center of the inhabited world correct?

In the early Middle Ages (VI-IX centuries), there were essentially no large, strong and developed states in Europe before the advent of Charlemagne’s empire. Consequently, Byzantium had cultural, political and economic superiority over the new kingdoms of that time (Franks, Burgundians, Ostrogoths, Bulgarians). She had a strong army and navy, Byzantium controlled trade routes in the Middle East, in the Black and Mediterranean seas.

For the 6th-9th centuries, Constantinople was the richest European city, it had walls that were unique for that time and was well protected from the sea, so the chances of taking it by storm were extremely low. Contemporaries considered it the center of the inhabited world, since the chroniclers of that time had vague ideas about other developed powers in India and China, and against the background of Rome ravaged by barbarians and the small capitals of new kingdoms in Europe, Constantinople looked very solid.