Regarding comparisons between the US and other countries, they may not be as relevant to how people feel than what people see in the future for themselves and their kids.
In other words, if they see themselves or their kids getting poorer in the future, they may be quite unhappy about it, even if the future level of income and wealth is still high. For example, suppose a typical forum demographic family that does not get college financial aid (meaning income about four times the US median household income) experiences job loss(es) and ends up with a lower income of “only” twice the US median household income. Such a family is likely to be quite unhappy. In contrast, a family who was previously making the US median household income who experienced an income gain to twice the US median household income is unlikely to be similarly unhappy.
The same happiness/unhappiness may apply to parental views on their kids’ futures. The typical forum demographic family may be unhappy if their kid settles into an adult life earning “only” the US median household income. A poor family may be much more satisfied if their kid ends up in the same place. Of course, for the typical forum demographic family, there is much more room for downward mobility for the kids than there is for upward mobility. That the economy may be turning negative-sum for all but the plutocrat class would be another factor making downward mobility more likely for most people. Local economic conditions may also be an issue, even if the overall economy is doing better.
Then throw in that greater economic inequality and a weaker social safety net means that the stakes are higher in terms of reaching a higher income. So it should not be surprising that such an economic environment would drive parents to try to give their kids as many advantages as possible (starting in early childhood) in a more competitive economic environment.