[watwut]

Social mobility is defined somehow and that somehow is not "the absolute total measure of fairness of any society". And speaking about virtually any country in the world, including North Korea, they all have lower class and upper class. Your worry about totally classless society is purely theoretical.

If we would live in classless society, social mobility would be less important measure.

Plus, you define achieving the limit of the talent in purely financial form. If I am genius mathematician, achieving limits of the talent mean doing great (potentially useful) math somewhere at the university. That does not translate to neither "high class" nor "rich".