Although they were a very ambitious people, the Greeks were not much of a numerous people compared to say the Germans, the Irish or even the Arabs and their reach is small compared to other ethnic groups. In Anatolia, the Turks managed to keep their own language and displace/assimilate the local Greek-speaking Anatolian population while adopting a lot of the culture.
The Greek language was at various points throughout history very widespread but not so much in recent history. Greek-dominant states such as the Eastern Roman Empire or the short-lived Argead Empire and its Successor kingdoms failed to last enough to leave multiple successor states speaking languages or dialects derived from Classical or Medieval Greek the way that the old Latin-speaking Roman Empire, or the Arab Caliphate.
So do we increase the numbers of Greeks? I'm extremely flexible so we can have PODs going as far back to the time of Alexander the Great's coronation as King of Macedonia or even prior to it. If it's possible, I'm curious if this is even doable after Osman proclaimed his independence from the Seljuks and set in motion the rise of the Ottomans.
How do we get a large number of self-identified Greeks?25 million? 30 million? 40 million? 70 million? 100 million? 200 million? 300 million? More than that.