I always assumed it was tubes in recording studio responsible for vast majority of difference, early SS not so good. I'd think you'd have to directly compare recordings both produced in tube based studio, one with dolby, other not. Dolby came in around same time most studios switching to SS, so is it the Dolby or SS? Without something in recording notes pertaining to Dolby, how are we to know?
And then the multi tracking creates synthetic sound stage. When I think of the 50's and 60's recording I love, I'm thinking about the virtual live in studio recordings. Natural ambience, timbre, can't beat these for performers in room sense on playback.