Well, I agree to your point that Pakistanis are not descendants of central asian invaders But I disagree with your point on conversion of faith. Instead conversion of faith is the act of bravery. Leaving the faith that your brothers, fathers, forefathers is not easy. You do it when you are convinced that your old faith was untrue. Today, if any muslim leaves his faith and becomes athiest, muslims will call him "Kaafir" but nobody can take away that even if is Kaafir but he is brave. Knowing the fact that how wrong others will think about him, how his own society will think about it and may even kill him for that.
So changing faiths always takes courage.
Edit: Also, do you think your forefathers were hindus for eternity ? Humans are on this planet for millions of years, there were certainly 1000s of religions / faiths / beliefs that would have come this way. Thinking that Hinduism is the first religion on the planet is another hilarious lie. It could be said that it is the oldest "known" religion but ofcourse it can never be the first religion .. What was here million years ago is anybody;s guess.