> When SEC approved Enron's change in account reporting practices from historical cost to mtm, I would argue that the SEC failed it's mandate to protect investors by allowing disingenuously optimistic instrument valuations

In a broad sense, sure. But that means making the SEC both an auditor and determiner of fair value. Even after the ensuing flurry of rule making, that is very much not part of the SEC’s remit.

There is a reasonable debate to be had around whether it should be. But the SEC not double checking auditors is not evidence of its lawlessness.