A lot of the earliest stereo recordings also have hard-panned elements (drums all on one side, bass on the other, etc.). I don't know if you've come across any of that yet but it's kind of annoying to listen to on headphones, especially ones with decent enough imaging and soundstage that the unnatural, isolated positioning is painfully obvious.
As far as equipment, they did have different stuff back then (tubes were a lot more prevalent until at least the 70s when solid state was being widely adopted), but what's even more different is the way it was used. Modern recordings often employ a lot of volume compression and sculpted EQ enhancement to create a "produced" and "big" sound, as well as Autotune and other studio trickery to produce "perfect" takes. Back in the day they had none of that, and the upshot was that performances were a lot more natural and filled with idiosyncrasies and slightly "off" bits that added character but, as you've found, will show up with highly resolving audio equipment.
I prefer well-done old production, warts and all, to most of what goes on today. That doesn't mean that all modern production is bad. Up through the mid-90s a lot of it was pretty decent, and there are still some well-produced albums put out even today. Unfortunately, these days they mostly just try to make it as LOUD as possible without any attention to natural attack and decay, probably because only a tiny minority of people have anything better than a boombox or an XXXXXXXXXXXXXXXtra UltraBass eXXXXXXXtreme mini system and thus can't hear what's been sacrificed for the increased volume.
You've got that to look forward to as you climb up the equipment ladder. Some albums will just sound terrible, and there's pretty much nothing you can do about it except try to enjoy the music anyway. On the other hand, other albums will reveal unlocked potential, and that makes it all worth it in the end.