The last Italian emperor ?

[Jona Lendering]

But it seems one man from the motherland occassionally reached the top up to at least the
5th century AD, judging from your learned responses.

I would guess that Italy was in fact returning to the top, precisely because it wasn't the top any more. You can see a parallel development in the imperial residences: in the fifth century, we see nearly all of them residing in Rome. Italy was becoming a world of its own, and more powerful rulers were living in Trier or Constantinople.