You and I are looking at roughly the same time period from two different perspectives. You, the seasoned professional & me, the advanced consumer. And I found that time slot to be very interesting. In 1970 Mati Otala raised the issue of TIM distortion. But it wasn't until maybe mid 70's it became real interest to audiophiles. There were many main stream products that started listing slew rates and addressing that issue. Then came the interest in the ubiquitous coupling capacitors. Suddenly there was great research as to what might be the audible outcome from capacitor DA/DF/ESR and inductance. All of a sudden there was an abundance of main stream & high end companies offering their version of "direct coupling".
And how might gear like audio power amps benefit from independent power supplies? Straight line tracking tone arms went main stream on Harmon Kardon & other TT's. And if CD-4 had waned it brought the benefits of better vinyl composition, half speed mastering, and improved stylus design to the masses.
All of these alone could only potentially bring smallish improvements but as a sum the potential for improved sound & I embraced it all trying to learn & separate the wheat from the chaff, so to speak.
I must agree with you on that! Even analog TV is an amazing feat, keeping scan lines synced, blanking intervals, and then shadow mask tri-gun color TV. Wow! I think the big break through , besides home taping, was the Advent VideoBeam projector:
Yeah, I do remember some noise about Transient Intermodulation Distortion, but honestly, I don't know if anyone ever honestly heard the difference.
One project I worked on, I decided to see what would happen if I just took out the coupling capacitors between the stages, and it was fine, although I think there were a few guys there who felt it wasn't "good practice." The voltages across the caps were always under 1V, and I think there were four of five of them. It might have reduced the dynamic range of the unit by 1db, just because of the clipping point.
But seriously, are "modern" designs audibly better than the Crown DC300A? I know they have issues, but they were the high-fidelity beasts of the early 1970s.
I went to a closed-circuit showing of the 1965 Indianapolis 500. IIRC, it was at the LA Sports Arena, next door to the Coliseum. There was a video projector there (I couldn't get close enough to it to find out anything, and even if I could, that wasn't a big interest of mine at the time) that put up a picture of about 25' diagonal measurement. Of course, the arena was dark, and the picture was monochrome, but it was so cool because it was the Indy 500!!
A couple of decades later, I actually designed an AV system with a color video projector that used a 25' diagonal screen. It was a GE Talaria model, and I thought it was remarkable. We had installed several three-tube projectors in systems before, and aligning them was a job that took a few hours - usually all afternoon. The GE didn't have that issue, and it put out about ten times as much light as the 3-tubes did. That project had a lot of fun elements in it, and I got to play with all the big-boy toys!