Perhaps you are right! You are not alone thinking such , i had read it a lot and it is the reason why i bought my Sansui and my AKG K340 products born exactly at this era end.
Nobody ever build an headphone so complex after ( too costly to design it well said Kennerton guy )
And i dont think that many amplifier of today beat the Sansui alpha in the range quality pieces, quality design and price today...if we transpose inflation cost...
Anyway for cheap and low cost good product we cannot beat our times i think ...
But i am not an audiophile market specialist... 😊
1950s into the 80s. Tubes were plentiful and inexpensive. Everyone built their own amps. Recordings were crystal clear. Folks sat around and listened together. Music was awesome.