You are right. According to wikipedia, in 1922 only 231,000 Armenians were still living in Turkey (of a population of over 1.5m), over half of which lived in Istanbul.Their's no way that would happen for one very big reason, by the 40's their were only a small amount of Armenians left in Turkey, as in less than 50,000, and a good portion of them were Muslim (hence why they stayed in Turkey), further more unlike the partition of Germany, their were simply not enough Armenians to fill any 'new lands' without causing Armenia itself to become nearly depopulated.
However, this hypothetical Armenian state doesn't necessarily have to be populated by Armenians.