Throttle cut or mixture cut is irrelevant to this accident. The ATSB laid the blame at the feet of the ATO for initiating the exercise "when a safe outcome could not be assured"
The ATSB quote a CASA guideline not to do asymmetric below 1500ft after dark.
Further, I would suggest that it was not conducted "just after dark" since the ATSB say they did not take off from Bankstown until 16 min after last light. They then flew to Woollongong then Cambden. So it was properly dark. And anyway, dark is dark. Its a binary state after last light.
Its a bit unusual for a 16,000 hour ATPL to be getting an initial issue MECIR. One wonders if the ATO overestimated the candidates experience in these circumstances - especially since this was the first and only flight the ATO had with the pilot under test. Which is another risk management warning flag the ATO ignored.
This accident is about poor practices by the ATO, not mixture cuts, throttle cuts or even really asymmetrics. It has no more logic than cutting power on a single in the same circumstances. Its about not clearly understanding how to achieve the training objective in a low risk manner.