The suffix -iye, however, is also a suffix that is used in Turkish coined words of Persian and Arabic compounds where it means -ness or -ity: https://en.m.wiktionary.org/wiki/یت#Ottoman_Turkish
There is kurabiye (gulabiye = gulab (rosewater) + -iye), and later coins such as cumhuriyet (cumhur (general public) + -iyet).
Türkiye is not such a coinage. In Ottoman Turkish Türkiye would mean Turkness.
I don't argue with people who identify as Turkish or German. I don't know if Sahin identifies as either or both. I know that it is harder for Turkish immigrants to get a good education in Germany, especially during the time he grew up in. I also don't care much about the debate of how useful immigrants are, because the result may very well be that they aren't on average that useful and that quite a large portion of criminals are immigrants. Usefulness or consequence to society should not matter for the rights of an individual. And immigration control always comes down to violating someones rights in order to somehow get rid of them if they are unwanted for some reason.