I have several direct to disc albums. Between songs, you can clearly hear as the musicians would change the music. Various noises, breaths, etc are present. Sonically, they were the pinnacle for vinyl records in their time. Musically, many were just ok. Many were mediocre. A few were very good. I remember reading about sessions being ruined by a simple mistake. A cough, a dropped object, someone's miscue. That's all it took to scrap a side. Playing 15 to 20mins without a flaw is tough, there's no going back and fixing it. Toss it and start over, and pay the musicians for extra time, along with the mastering engineer, mixing engineer, another cutting lacquer. It can get expensive, and you only end up with a few thousand copies from the 6 or 8 stampers made from the single master and maybe 2 or 3 mothers. Since they were going for a premium product, numbers were more conservative than your normal commercial records.
There are lots of things I don't miss about records... cleaning the record before playing, clicks and pops, wow from a slightly warped disc, adjusting the cartridge to get the optimum angle, getting up every 20 minutes to change the record.
Once digital tape came into play, you got almost all of the advantages of a D2D setup, but you could make as many as you want. Just play the tape back and make a new master when you need it.
RE mixing on "Sh*tty Speakers":
There were quite a few magazines about audio back in the day. Audio, Stereo Review, HiFidelity, HiFi News & Record Review, Absolute Sound, Stereophile, Audio Critic, What HiFi. They often had interviews with record producers, engineers, etc. I don't ever remember a producer or engineer saying "I make sure I check the mix on a shitty system so it sounds ok on lousy stereos", or "I always check my mixes on a transistor radio" since in the early 60s, eveyone had a transistor radio, strictly AM and with a 1.5 or 2 inch speaker. If you were a serious music lover, you were expected to have made a moderate effort to assemble a quality system.
The change in the audio industry was MASSIVE over the 10 yr period from 1958 to 1968. There are archives of magazine from that period on the internet. Heck in 1958, stereo records were a rarity! I wish some of the younger people would go back and see how things have changed since those days. It might give some perspective on how things used to be done.