I think the SSL compressor is SO much a part of the sound of so MANY pop hit records that it becomes, even subliminally, the sound in your head for a certain type of record.
That's why I use it for those types.. not to make it sound like it's already on the radio (which is a whole OTHER level of travesty) (or "whole 'NOTHER", for you, Terry, I know you're a proud Southerner <g>)
You're certainly right that many of those classic records, especially for us older guys, were mixed without stereo compression (or mono compression!) on the mix.
But often they were compressed at mastering, so it's only a question of WHEN.
At some point, some of us decided that the sooner our records sounded 'finished' in the process, the more likely the A&R weasel (speaking as a former weasel, I can say this blithely) or record company president or the band's manager or agent or whomever would like it and think it's finished as well.
So I started mixing through compressors in about 1975.
At that time, some people thought it was a lot of compression. But in comparison to what is now the norm, it was next to nothing... and my records tend to be on the less compressed end.
But it's all a matter of taste.