I've never understood the Dolby switches. I had a good number of tapes with noise reduction via Dolby B but when I turned on the switch to compensate for it the sound was rolled-off and boomy. My tapes always sounded best -- and like the music on other media -- when played without the Dolby switches.
My tape experiment was pretty short-lived. Only significant discovery was Stoneage Romeos.
When I said that tapes had high fidelity I meant prerecorded tapes. For a while (as "Tower Records and Tapes" suggests) LPs and cassettes were considered pretty much equivalent.