Back in the late 70s there was a race by the major electronics manufacturers (Pioneer, Kenwood, Sansui, etc.) to lower Total Harmonic Distortion or THD. Sales were often driven by these numbers and lower THD was a great way to generate interest in upgrades. As new electronics were coming out with ultra-low THD many listeners began to notice that the newer gear actually sounded worse (harder edged, less musical and more electronic sounding) than similar previous models which had higher THD.
Engineer Matti Otala from Harman Kardon then discovered a new type of distortion called Transient Intermodulation Distortion or TIM, which seemed to correlate to the negative sound attributes heard with low THD designs. He found that decreasing THD which was commonly accomplished by adding negative feedback created higher TIM which was believed to be more harmful than the higher THD. So many of these manufacturers then started cutting back on negative feedback and TIM became a measurement which was often included along with THD.
This demonstrates how just focusing on measurements can be counter productive, in that we may have errors in measurement due to test equipment limitations or we may be measuring the wrong things. Who knows how many other forms of distortion may still be unknown that can have an effect on human perception of music reproduction.
Many of the receivers from that era are being serviced and sold for very high prices, with sellers saying "they don't make them like they used to!" and playing up the perception that larger and heavier electronics must be attributed to their high quality. The truth is that many of them don't sound good at all due to the focus of their initial designs during that era.