[stavros]

Modern Greek doesn't have the French "u" sound, I don't know if ancient Greek did. The "υ" in "κυβερνήτης" (cybernetes/kubernetes = helmsman, governor) is pronounced "i", as in "miss".

Incidentally, the word "governor" comes from "kubernetes" as well.

[mathieuh]

The French "u" sound is just "i" pronounced with your lips rounded, so the two sounds are very similar.

https://en.wikipedia.org/wiki/Ancient_Greek_phonology#Vowel_...

It seems some varieties of Ancient Greek did have that sound

[stavros]

As far as I know/can see, it was more of an "oo" sound, rather than a ü, but I'm not an expert and you may be entirely correct.