Well, defining a good recording would also depend on the intent of the recording. Your example of 70s rock has nothing to do with whether the engineers were deaf or drugged out. The recordings came out exactly as intended ... you just don't happen to own the type of system that those recordings were optimized for.

The biggest selling studio monitor in the 70s was the JBL 43xx series, and the best selling home audio speaker of that era was the JBL L100, which just happens to be the consumer version of that same studio monitor. Put two and two together and it's not hard to figure out that recordings from that era will sound best on speakers that emulate the characteristics of those vintage JBLs. Neither of these speakers were models for frequency response accuracy, but they were optimized for each other and many of the recordings that came out of that era. When I used to bring rock LPs to audio stores, I remember how horrid they sounded especially through the British speakers of that era. Sure those speakers sounded great with the more audiophile-oriented demo material, but who'd want to subject themselves to that kind of wretched music?

Plus, you have the various compromises needed because of the LP medium. While the LP can hold a lot of music information, the fact is that most people in the 70s were listening to their LPs through some rather horrific record players (remember the automatic record changers with the stack spindles?). Put too much dynamic range into the grooves, and you got tracking problems for the majority using lower quality record players.

This is no different than the 90s when the best selling studio monitor was the Yamaha NS10. As with the JBLs, the Yamaha did not have an especially flat response, but what it did produce was a very good approximation of how music would sound on a compact satellite speaker or car audio system, which made it popular with recording engineers. Given that the majority of pop music nowadays is heard through either a car audio system, compact satellite/multimedia speaker, or headphones, the NS10 was an appropriate monitoring choice for those genres. This explains why so much recent music sounds better in a car than on a good home audio system. If a newer pop recording sounds good through a higher resolution home audio system, that's more by coincidence than by intent.