WHat did Audiophiles hear during Tape deck era?

Actually the D6 sold for more than 750.– CHF in the early eighties, the D3 maybe slightly below 600.- CHF. They are built to last, except the tape heads, but the latter seem to be of very durable quality though.
So, 40 years later in todays value, in legendary Sony quality of then (they don't fabricate quality like that anymore) would cost as much as many of these "audiophile portable players" in the above 2000$ range, but without firmware & interface & standards obsolescence.
So 1500$ is a lot indeed, but still considerably less than what a 2020 equivalent pro cassette deck would cost new...

Cassette issues were horrible.

Still recordings on your own were missing something.

i had extremely good results with a Mits  hifi  VCR for recording albums.

Whoa! Opinions are all over the map. 😳

Reel-to-reel tapes really took hold in audiophile-land in the mid-late '50's, when stereo was introduced and it took an R2R recorder to buy and play stereo.  R2R decks stayed in many audiophile decks right up into the mid-to-late '70's, when stereo cassette decks started to become good enough (with new tape formulations and eq's) to be "acceptable" on a high-fi rig.  At all times during these eras there were both "audiophile quality" pre-recorded tapes sold and a lot of convenience copies of discs.
Take it from one who was an audiophile through it all.