What simple method would you use instead? It is effective to have such comparisons for quick communication of the relative size of things.

It is effective but wrong. It is the same as to compare a river flow to dam volume. There is a relation, but does not mean anything.

A better comparison is to compare somebody's net value to the total housing value of a city. For instance comparing Musk's net value to the total value of all the houses/apartments in New York. Or the the value of the gold in Fort Knox.