I was asking you to define the premises under which you are arguing, not to defer to some abstract third party.
Wealth is not a zero-sum game. Median household income in the United States has remained fairly stable in CPI-adjusted dollars since the mid-1970s, but in the mean time the population has increased by over 100 million. In other words, the "middle class" has grown by millions since the 1970s. No one in 1976 owned a cell phone, whereas practically everyone does nowadays, and food prices have generally increased at a slower rate than CPI. Hence, nowadays the "middle class" can afford food more easily, and can afford luxuries that the "middle class" of the past could not. Moreover, these facts are true regardless of the income quantile under discussion.
The existence of high-paying jobs is predicated on the ability to create a lot of value through work. But value is relative, and changes over time. Nowadays, it takes a fraction of the number of people to build an automobile that it did 50 years ago. And there are people outside the developed world who are willing to do it for a lot less money. But even if you try to ignore them and their equally legitimate desire to earn a good living, the unstoppable changes in consumer expectations and efficiency cannot be ignored. The same jobs just aren't as valuable as they were before, and there's nothing that can be done about it.
But there are always new jobs. Focusing too heavily on some idealized version of the past, to the point where you create economic stagnation, only leads to ruin. Every system that tries to set wages and employment levels too far away from market equilibrium increases, rather than reduces, inequality and suffering. Most places have begrudgingly averted such folly despite flirting with it time and again, but some have not: Detroit, as I already mentioned, also Zimbabwe and Venezuela.