What you're saying starting with Leica, and then "Nikon came along" is at the root of my comments about this article. There are more than 40 years of innovation between the ur-Leica in 1914 and the Nikon F. For a famous example, have a look at the movie "Rear Window" (1954), specifically the still shots of Jimmy Stewart's character using an Exakta with a very long telephoto lens. The SLR made long lenses practical in a compact camera. But Nikon wasn't there first.

The Nikon SLRs picked up a reputation after being used by professional photographers to cover the Vietnam war years after the release of the first Nikon F. Were they professional cameras before professionals started using them?

I have failed to mention the Asahi-Pentax, released in 1957, which had everything the Nikon had two years later. Why is the Nikon F the first professional 35mm camera? What made it special enough to obscure years of camera development?