Where did you get these ideas? The OMs were backed by an extensive sysetm. The F2 was an improved F, the F was and is quite a rugged camera. In the US the Spottie may have been seen as an amateur camera, elsewhere working pros used them.
Point by point:
I have never seen something called a system camera unless it had fully interchangeable viewfinders and actually had a system of multiple different viewfinder attachments.
You misunderstand me about the F2. I mean pros upgraded from less rugged cameras to the extremely ruggedized F2. The F2 is about as rugged as it gets in a system camera, right? They certainly outsurvive a lot of the contemporaries.
I still can't get my head wrapped around a pro using a stop-down metering camera with regards to the Spotmatic and other high-performance M42 cameras like the 1000 and 2000 DTL. I was always under the impression that with the exception of Nikon F and Beseler Topcon early adopters, most photojournalists at least kept using rangefinders until wide-open metering became ubiquitous in the late 60's. Is that not how it went?