Defining what Greek food really is can be trickier than we might realize. Greek cuisine in the United States, in general, seems to represent what was common in Greece when the families came over from Greece, and this ranges from late 1800's or so to today. These recipes were then handed down through the generations. Meanwhile, the cuisine in Greece changed and evolved and modern Greek cuisine looks much different than those recipes of the past.
My family came to the United States just before World War I, so our family recipes appear to be stuck in that time. I've been to Greece enough time to know that the food in Greece now is different. In my family's case it is less about being "Americanized" for the most part as it is that the recipes and foods are old and possibly from another time in Greece.
Immigrants In the United States have also forced to adapt the foods because Greek ingredients like Mastic and Mahleb, that are key ingredients in many foods, weren't common, so the families maybe started to use vanilla extract and cinnamon instead. I know that my family's "tsoureki" uses cinnamon and orange instead of mahleb because of the difficulties in obtaining ingredients, and the few times I have tried to add mahleb instead, my family was confused and it didn't go over very well. I don't think there is a right or wrong way to experience Greek food because even in Greece, you have regional and familial difference.
I believe the fusion foods we see right now are a good thing. I would rather Greek flavors make their way into other foods than not because it is a flavor profile I know and love!