As indicated in the article, moving dashboard data files from compressed-and-slow NAND to a slightly-less-slow regular HDD would definitely be a performance win, but I think the author underestimates the extent of the improvement.

The dashboard is commonly accessed right after the system has booted, at a time at which lots of startup processes are still competing for files stored on the NAND OS partition. This dramatically increases latency, and thus load times. Fetching dashboard resources from an idle HDD partition could definitely improve responsiveness by more than just a few milliseconds.

I'm not too sure about the exact tooling available for the Xbox, but regular Windows has lots of tracing and analysis options available to improve boot times: see, for example, https://learn.microsoft.com/en-us/windows-hardware/test/wpt/...

I would not be surprised at all if the Xbox team made this change in response to detailed responsiveness metrics, and that they saw a definite improvement afterwards, which is why they shipped the 'attempt'...