The Byzantines had long been in firm control of the historical region of Macedonia because it hosted an overwhelmingly dominant Byzantine Greek population. The Slavs were driven out after the Byzantine reconquest, and whatever Slavs remained Hellenized, something made possible thanks to Christianization. The driven out Slavs likely moved to Kutmichevitsa, and eventually, their descendants streamed back into Macedonia during the late 18th century.

In short, FYROMIANS have nothing to do with ancient Macedonians whoever they were, they were solidly part of the Greek ethnos for centuries and centuries. In those centuries, they also tried their hardest to prove their Hellenic ethnicity to the Greeks in the south. The FYROMIANS are a mixture of Illyrians and Thracians + Slavic migrants, the occasional Roman colonist, Vlachs and some Slavicized Greeks. That's it.