This doesn’t say eliminating discord reduces those inequities. In addition, the editorial doesn’t claim constant economic expansion will reduce the total amount of discord in a society—just that a failure to expand will cause divisive political factions to become stronger.

This exception to the rule doesn’t disprove the rule. It doesn’t change the editorial’s premise that divisive political factions make good governance harder to achieve.

This strengthens the editorial’s assumption that improved economic mobility will make class divisions less stark. It rules out a damaging possibility: that economic expansion mostly helps higher-income people, making class divisions greater.

If anything, this weakens the argument. It suggests that economic growth may be self-defeating in the long run, since reducing class divisions may reduce the number of very wealthy people willing to invest.

This doesn’t address the editorial’s primary assumption: that improved economic mobility decreases class divisions. It suggests that failure to expand the economy is self-reinforcing, not that it leads to bad governance.