20 Year Old Amplifiers compared to 2017

Amplifier technology reached maturity in the seventies, when output transformers were abandoned in solid state amps. Ever since, well designed amplifiers used within their specifications have exceeded human hearing acuity.

This statement is false.

Humans can easily hear the distortion of most modern transistor amplifiers. The brightness and hardness of solid state is well-known and a topic of endless debate- the brightness and hardness is the direct result of the fact that the human ear/brain system uses higher ordered harmonics to sense sound pressure. The slight amount of distortion is converted by the ear to a tonality. The ear has to be keenly sensitive to these harmonics because of the wide range of human hearing (140 db). So its far more sensitive to them than the lower ordered harmonics.

If anything has changed since the 1970s, its our understanding of human physiology. The audio industry has been a bit slow to respond to that knowledge though, probably because the facts are a bit of an inconvenient truth.

If they haven't had a set of new capacitors installed, the 20-year-olds will be at a distinct disadvantage in any listening comparisons...

I doubt the "better offerings" sound much different in most cases  though no two cases are probably exactly alike due to all the variables at play.

Major advances in amp technology like Class D amps are the big difference. These put more offerings in that "better offerings" class that are much smaller, much more efficient and often lower cost. These things together make them more practical for many more than the better amps of the past.  I know it has for me.

willemj is right.

besides Class D (which allows less expensive and lower power amps), Benchmark has licensed some exciting technology in just the last couple of years which greatly reduces crossover distortion (so you don't have to try and run in Class A all the time)

atmasphere did not note that we had tubes back in the '70s....
- which burn a lot of power