Why turn this into a vinyl vs CD war? There's been other threads for that! (And for anyone new to this, it's been hashed out numerous times.)
As for older gear, it may be some of it was built better, or used a superior design.
That does not mean older gear is intrinsically better. Generalizations have their uses, but I don't think this is one of them.
Also, in my experience, the reliabilty of most electronics has improved quite a lot. As has the quality of manufacturing, overall.
The circuitry in amps, near as I can tell, has been the same general design for all of my lifetime. A three stage class AB amp with global feedback seems to be the most common amplifier. Of course in my lifetime, class D showed up in receivers, but the idea was not better sound, it was better efficiency, so I don't see where that enters into this discussion?
The coolest part of old gear is their look. I loved all the dials and switches. The good quality units used really nice mechnical parts, and had lovely user feedback. You don't get that with most modern gear.
Older stereo receivers did not have to drive 7 or more channels. The power supply only had to drive 2 channels, and some of those receivers were beasts. I seem to recall some of the old Kenwoods weighed over 50 pounds, and had impressive bench specs. It's not like all receivers were like that. Just like now, there was cheap junk.