The idea is that you get a lot of elites which are highly educated and expect high positions in society, but end up bitter because reality falls short. Engineers break with this because in general they are actually quite well compensated.
The targets of the theory are essentially people with non-stem post-secondary degrees
From Wikipedia: >Elite overproduction is a concept developed by Peter Turchin that describes the condition of a society that is producing too many potential elite members relative to its ability to absorb them into the power structure.[1][2][3] This, he hypothesizes, is a cause for social instability, as those left out of power feel aggrieved by their relatively low socioeconomic status.
Im focusing on the USA, where engineers, STEM, and the like have high social standing, and do relatively well economically. Your "scholarship on the subject" is from 2007 and is from before the term elite overproduction was even coined.