Bojack, I see no basis for having any doubt about Mark's statement. For several reasons:
1)In my book, his many posts here over the years have earned high credibility for the perceptions he reports.
2)Operating temperature, which obviously would be affected for some amount of time afterward by an interruption in power, is fundamental to the physics and the performance of both analog and digital devices and circuits.
3)Overwhelming anecdotal evidence attests to the significance of warmup effects, in some cases over periods of many hours or even days.
4)If digital circuitry or processing is involved, initialization, resets, clearing of memory, the effects of temperature on risetimes, falltimes, and propagation delays, and other such things that occur when power is cycled can affect both those circuits and coupling of noise from those circuits to analog circuits. For example, I presume you've had occasion to see at times how computer behavior can sometimes be affected or corrected by rebooting.
I say all of that, btw, as someone who I doubt would ever be accused of being at or near the extreme "believer" end of the "believer" vs. "skeptic" spectrum.
And, frankly, your concluding phrase was entirely uncalled for regardless of the correctness or incorrectness of what you or Mark had to say.
Regards,
-- Al