>Is he now more concerned with protecting shareholder value? Who cares.
It doesn't sound like he's concerned with waste. It sounds like it's a typical Carmack argument - distilled and hyper logical, and his conclusion is more to do with the pointlessness of it. He actually concedes the point that the project may have been highly efficient (which it may or may not have been, he was steelmanning).
His main points seemed to be:
If every cycle matters and efficiency is paramount, just make the project monolithic C++ code. If every cycle matters, that is somewhat incompatible with general purpose OSs, and if it doesn't, the existing landscape is more than good enough. Presumably, he's calling out the absurdity of counter-arguments which are being unrealistic about the objectives of creating a new general purpose OS, while also focusing on extreme efficiency. He states that the requirements to fully achieve these objectives would require a "monastic coding enclave" like Plan 9 OS, and it wasn't realistic even with the high talent in Meta.
And that plays into the second point, which seems to essentially be "new OSs aren't a draw for developers, they are a burden". This is painfully obvious when looking at the history of OSs and software, and it's the obvious reason why "let the kids build their operating system ffs" should result in a reflexive "noooo..." from the greybeards. The deeper point though is that if A. is achieved, the B. Burden on devs will be even more onerous. Therefore unless the entire project is committed to truly moving crowds to new paradigms (good luck, literally billions have been lost here), just use the proven, faily high performance options that have widespread support.
The conclusion is "on balance, it's a bad idea." He's arguing it sharply (although I understand a Carmack steelman is intimidating to attack), but in essence it's a fairly banal and conservative conclusion, backed with strong precedent.