I wish we had the data to support those opinions or beliefs as they just that.My personal opinion was older Naim was beatifully constructed in the traditional 'belts and braces' UK school of design, but poorly performing, fragile and prone to failure, due to inadequate cooling, poor component choices and simpy overpriced by the time it arrived down under.
However, I agree that NAP250 had inadequate cooling but it was not fragile. It simply cut off if heated. You would be hard pushed to over heat it in a normal domestic use. I never managed mine. If you needed a professional amplifier or had a none-domestic use case then you would buy the NAP135, which was mono and had a fan. Horses for courses…
Can you elaborate on your “poor component choices” comment please?
Finally, early Naim power amplifiers were based on a sample design from the RCA manual for the 409xx series transistors. The only difference is the delay on the protection feedback and regulated power supply. Especially the latter was the main reason the amplifier sounded louder than most because when clipped there was no double mains frequency modulating the audio.