But you see, tragedy is subjective. I assure you, you would be more distraught were your house to burn down than, say, the Uffizi Gallery or the Library of Congress. People tend to respond to personal tragedy on a completely different level because it is more acute.
You would have the reaction of any human being. Self-pity, fear, anxiety. Whereas towards a museum fire you might feel a dulled, vague, undirected distress.
The point being, no matter how honest and well-meaning your example is, you will never convince someone that their grandmother is less important than Terry Pratchett based on the fact that she probably never wrote an expansive series of science fiction novels (or any other fact, for that matter).
While I understand and, to an extent, agree with your point, I see less harm in dropping the argument entirely and focusing on the author's ailment.