The main way that a country gets richer than another rich country has to do mainly with one thing. This thing is its name value. Switzerland is more widely recognized than Luxembourg. You rarely hear people say “I want to go skiing in Luxembourg.” Usually, when someone thinks of a skiing resort overseas, they think of Switzerland or some other popular countries. This makes Switzerland richer than Luxembourg.
From time to time, someone will travel mainly to a popular country to vacation in like Switzerland, but they will travel for one day to Luxembourg to tour and do activities. Therefore, the popularity of a country is the most important thing when comparing their economies to each other. It would be like comparing apples to oranges.