Your claim doesn't pass the smell test. Pay levels are set by a giant, uncoordinated, massively competitive process.
If you know any software engineers who are grossly underpaid for the value they can provide, hire them! Then "underpay" them just a teensy bit, instead of the "grossly underpaid" exploitation they suffer under now. Pocket the difference for yourself, as a reward for seeing their true value so much better than every other employer.
It seems to me you believe very strongly in a black-and-white world where "the market" functions just fine. It is terribly out of sync with actual evidence, though, which you simply brush aside while scribing arguments containing numerous unsupported assertions and demands that others support their statements. As if we should simply accept your point of view as the truth by default.
You know who wasn't part of the alleged cartel? Facebook. Microsoft. Yahoo. Amazon. Oracle. Salesforce. Twitter. Yelp. Autodesk. HP. Cisco. VMWare. AMD. Workday. Electronic Arts. Zynga. Netflix. Etc. Etc. Etc.
Also, no seed- or VC-funded or YC-backed startups of the past 10+ years were part of the cartel. Also, no consulting/contracting shops were part of the cartel.
You seem to be applying some sort of undifferentiated-laborer/factory-floor model to a region/industry where it doesn't apply.
There certainly are market failures; when they happen, they can be studied and quantified. There's no evidence of that here. All we have is angry crusaders with grandiose damage claims, who probably weren't even affected by the no-poaching agreements.
An it is statistics 101 that if you change the skewness and kurtosis of a distribution if effects not just those at the top.