I heard once theory that romans moved alot of population from Palmyra (Syria) and Nabatea to Greece once, so that's why ancient greek people are not exist actually in Greece anymore.
I am not sure about that theory though...
Yes, today's Greeks have nothing to do with the ancient Greeks. I have even an entertaining story about that:
... It happens during the Occupation era of Istanbul (about 1919, by Englishmen, French and Italians).
At the university of Istanbul, when the Turkish professor of History enters in the classroom to teach Turkish History, Greek students (supported by their monkey armenian friends) stand up and say "we don't want to study your 'barbaric' history, let's talk about the magnificient Greek History and Civilization".
The answer of the Turkish teacher is amazing and relevant; "Yes, I'd talk about ancient Greeks, but what is the tie between you and them? You only are scum of Romans, heavily mixed with Albanians, Slavs, Northern Africans; don't be proud! Ancient Greeks are all dead!
Yes, I support entirely the Turkish teacher. Atsiz Ata says that too, "when, in 1821, the so-called Helens rised up for their independence, in the village neighbouring Athens, the spoken language was Albanian; these people have been Helenized systematically".
Moreover, recent genetic studies would have found Sub-saharian genes among Greeks. I think it's true. The only laight-haired and light-eyed among them have Albanian or Slavic blood. They aren't nice people.