Increased stratification started when incomes decoupled from productivity growth in ~1979. That was caused by a wave of union busting.
Are you presenting this as opinion or fact?
Maybe? eg. something like "subprime mortgages caused the 2008 recession" would qualify as a fact. Maybe what the parent poster said was the academic consensus among labor economists, or is at least a serious competing theory among mainstream academics (ie. not something that only a few marxist economists believe).
Example: https://www.jstor.org/stable/1240452
The USSR bought grain when its harvests failed during the 1970s - this is not the action of a superior system about to surpass you and replace you.