I think the final paragraph points out the obvious point - social mobility has never really fully existed. Previously large swathes of the workforce were never

I think the final paragraph points out the obvious point - social mobility has never really fully existed. Previously large swathes of the workforce were never expected or enabled to progress - women and ethnic minorities. When they are included I doubt the golden age looks so golden from the point of view of "everyone" suddenly getting rich off the economic returns of work. Now the economy is much more open to merit - the problem with meritocracy (as the article points out) is that once you open it to everyone whole swathes of people lose out. See the trends of successful women marrying successful men thus creating a more closed top tier of society.