You made a mistake in your logic. Let me modify what you said a little bit, "If there is no cure for a plurality voting system then there is no cure for any voting system, since a plurality voting system is just a subset of any voting system." I doubt you agree with that statement. A similar analogy to your cancer analogy would be: if there is no cure for cancer, there is no cure for anything.
You made a mistake in your logic. Let me modify what you said a little bit, "If there is no cure for a plurality voting system then there is no cure for any voting system, since a plurality voting system is just a subset of any voting system." I doubt you agree with that statement. A similar analogy to your cancer analogy would be: if there is no cure for cancer, there is no cure for anything.