I'll grant that there were some truly horrible sounding ones but I recall some of that Monarch pressed 70s stuff was really good quality - I'm thinking Billy Prophet, George Blackwell, Mickie Champion etc. Same with lots of the vinyl boots - James Barnett and Tamala Lewis off the top of my head.
I'd bet that loads of them would pas the blindfold test. Apart from the fact that many are trashed by repeated plays on crappy equipment of course.