Well what you’re calling left wing psudoscience is an article by Economic Policy Institute: https://www.epi.org/publication/charting-wage-stagnation/

They explain their methodology and data sources in meticilous detail, even more so in their report on how they do; https://www.epi.org/publication/understanding-the-historic-divergence-between-productivity-and-a-typical-workers-pay-why-it-matters-and-why-its-real/

If that’s not enough here’s some more stuff:

https://academic.oup.com/qje/article/135/2/645/572126

https://www.imf.org/external/pubs/ft/wp/2008/wp08185.pdf