As others mentioned this is a libertarian/crypto site so it's going to gloss over the loss of labor union influence that really sped up in the 70s (we can argue later about why this happened).

A correlation was graphed already, though it's comparing top 1% income share vs union membership:

https://en.wikipedia.org/wiki/File:United_States_union_membe...

This one includes graphs on the top 10% and also "middle-class" but i was only able to skim the article to make sure it didn't sound insane:

https://www.theatlantic.com/business/archive/2012/06/who-kil...