Around 1914, there were 15.0 million Muslims in the Ottoman Empire, as well as 1.7 million Greeks and 1.1 million Armenians. However, the Muslims included many Arabs; subtracting the Arab regions gives us a Turkish population of 12.7 million.
This compared to a population of 5.3 million in Greece (1910), which may have grown to 5.5 million by 1914. There were 1.2 million Armenians in the Russian Empire (1897).
So here are the approximate numbers as of 1914:
Turks: 12.7 million
Greeks: 7.2 million
Armenians: 2.8 million
Ratio: 12.7 million Turks to 10.0 million Greeks/Armenians (1:1.3)
Consequently, it’s not an exaggeration to talk of loose demographic parity between Turks and Greeks/Armenians, even without adjusting for perhaps 10% of Muslim “Turks” being Kurds. It was very possible for the Turks themselves to have been bottled up in the Anatolian heartlands in WW1.
Approximate numbers for 2017:
Turks: 80.8 million
Greeks: 10.7 million
Armenians: 3.0 million
Ratio: 80.8 million Turks to 13.7 million Greeks/Armenians (1:5.9)
Turkey has more than quintupled its population since the 1920s. In the meantime, Armenians had barely recovered from their genocide before getting hit by the demographic whammy that was the Soviet collapse. Although the Pontic genocide didn’t help, Greece did manage to eke out some meager growth – almost doubling its population – but has since gone into sharp reverse.
Consequently, during the course of a single century, the Greeks/Armenians went from demographic parity with the Turks to having six times fewer people.