Don't mind my excellent primary sources here as I quote wikipedia
"After the Monophysite schism and the Council of Chalcedon (451), both Melchites and Jacobites continued using the same rite. But gradually the two languages became characteristic of the two sides. The Jacobites used only Syriac (their whole movement being a national revolt against the Emperor),
No, not really. What gets forgotten now is that back then there were plenty of Greek speakers, including in Constantinople itself, who were anti-Chalcedonian (someone here has linked St. Andrew of Crete as going through an anti-Chalcedon phase), and there were Syriac supporters of Chalcedon. Severus, for instance, wrote only in Greek as far as I know, but his writings are preserved mainly in Syriac. The Jacobite movement wasn't a nationalist movement. It was a religious one.
and the Melchites, who were nearly all Greeks in the chief towns, generally used Greek."
The Melchites, however, were not confined to the main towns.
Can it thus be said that ethnically or genetically in some small way the Antiochians are different than the Syriacs? If the Antiochians are generally derived of Greek stock (city dwellers)
LOL. A lot of them where Hellenized Semites. Some made it to the throne in Constantinople, e.g. Leo the Isaurian (actually, Syrian), Nikephoros, etc.
and the Syriacs are derived of...well Syriac stock (local population)? Today you generally can't tell the difference between Christians (and Muslims too in many cases) in the Middle East by simply looking at their faces.
Telling the difference between Chinese, Koreans, and Japanese is easy for me (which is good, now that I have a Korean sister in law), but telling the difference in Religion based on faces (unless they are bearded or veiled), I've not been able. And I spend a lot of time with Middle Eastern faces.
" Another important aspect of his work is uncovering more information about how long the Syriac language remained in use Orthodox Christians in Syria and Lebanon– in some regions, the lectionary readings were only translated from Syriac into Arabic in the 17th century! Orthodox Antioch’s Syriac heritage has long been sadly neglected, but this is now starting to change…"
This is what I was referring to. But who knows if its actually true or if they were using Arabic well before this time.