His version of monopoly rent is a really convoluted solution to the question he poses as to why wages and productivity aren't connected. It could be completely true, but it's tenuous and likely not the entire missing part.

If productivity and wages are not directly correlated it would make more sense to see what was correlated with productivity gains and see how that relates to wages. Automation and process engineering are directly correlated with productivity gains according to the National Research Council. And automation is correlated with wage stagnation outlined here by The Washington Post.

So we see the correlation between productivity and automation, and automation with wage stagnation. There isn't another equation needed, and monopoly rent doesn't really make much sense in explaining this issue.