Religious connotation aside on this issue, I think Mehdi Hasan is and has been and will always be the greatest singer of Pakistan who will be remembered for centuries to come as such across the world by those who understand music.
(Many others were great but Mehdi Hassan is/was unique in Pakistan).
I have yet to hear a wrong note from his throat/mouth and have no reservation in saying that he did know how to sing.
The one and only…Mehdi Hassan.