Ghaznavi is a sensitive topic with Indians as i see it lol
Though I'l disagree with you here even though Ghaznavi has raided India he had never fully exposed India as we saw How well PRChauhan was able to defend India in the first battle of Tarain , the Rajputs were a strong force before that. Even he(ghouri) himself did not rule Delhi directly but now North India was a The go to Target for the invaders , it was rich and in a weak state meaning ripe for the taking.
On a sidenote you are right nobody can out a 100percent claim on his ethnicity though I'd point out that the Ghor tribe is Pashtun to this day