WHat did Audiophiles hear during Tape deck era?

Your choice was scratches or tape hiss. In the late 60's tape was better. There were bunches of pre recorded tapes and except for the hiss the machines were stellar. In the early 70s dolby came along and R to R machines like the Revox were being sold with it but interest in pre recorded tapes fell off and they all but disappeared from the market. Most of us just recorded albums. Turntable playback continued to improve. Now R to R is a niche market operating off rebuilt machines and ridiculously priced pre recorded tapes of very old stuff. It will fade as the supply of transports dries up and people get use to the inherent superiority of High Res Digital (appropriately mastered of course). There are some who will snuff up their noses with this assessment but I would be willing to wager that the R to R market will be all but dead in 10 years.   

A lot of scrape flutter and wow, pops and hiss. Mostly listened FM radio instead.

Recorded compilations from records through preamp onto CrO2 tape using 3 head machine. No Dolby. Played in the car on a Pioneer tape deck slung under the dash, hot wired to the battery, into separate amps for bass/mid and tweeters that were cannibalized from a pair of B&Ws. 2x10" sub in the trunk. No built-in stereo bs back then. Sounded vastly better than any CD or rip in any car since.

Always have played cassette tapes alongside my records.
Some pretty well pre recorded tapes around but the hot ticket is a top flight Nak deck fully restored by Willy Herman ( not as expensive as you might think but 12 month wait list!).
Use Fuji metal tapes and you have yourself a superb recording if the rest of your system is up to snuff.

I would tend to agree that just looking at paper specs and what we "think we know" ,that a tiny tape width running so slow that a snail can outpace it should not work to any acceptable degree.
Just goes to show that "what we know" means diddly squat at times! 

Cassettes really came into their own in the 80s and 90s. Dynamic range is the one thing that sticks out for me, cassettes are closer to the master tape than records or CDs. Also air and warmth. The digitally remastered cassettes are certainly more analog sounding than their CD counterparts yet more dynamic too. You CAN have your cake 🎂 and eat it too. 🤗