The only thing questionable about the Contax II or IIa was they had more piece parts than a Leica III. So they cost more to make, less profit for Zeiss.

They (Contax or Kiev) are nicer to maintain until you need a spare part.

All mine (including Kievs) with meters are still working accurate enough for Kodachrome - alas not needed.

Nikon copied the mount and rfdr from Contax sticking an N in front of the Ikon... rather cheeky. But cloned the Leica shutter. Replacing the rubberized fabric with titanium part way through SP production.

Leica went to M series viewfinder.

Canon cloned the Leica III until the VI and P (again steel shutter) then afterwards they went to Canonets, simpler, higher volume more profit, though they still did LTM professional models and lenses to '72

Yashica/Nicca ditto they even cloned the M back door.

They all went to SLRs for high volume sales, some sold better than others.

Cosina made modern lenses for Contax, Nikon and Leica (clones). Nikon did memorial cameras.

If you don't need fast reportage with a fast 35mm the knob wind and bottom load is not a problem.

If you do need fast then Nikon S3, or SP, Canon VI, P or 7, or Leica M all have lever winds and non rotating dials to not snag, (though the M is bottom load)

From 60-75 most hot news pros carried a Nikon F motor drive and 5cm /1.4 and a rfdr (from last para) with fast 35mm.

If you don't need fast reportage any of the old cameras are ok, but not all lenses are completely interchangeable

The old lenses produce lower contrast images pastellising colours, indeed many old lenses live on dig&@&@ cameras using adapters and many Contax and Nikon lenses live on M cameras, there is a cottage industry turning Kievs into (cheaper) M adapters, and parts Kievs are cheap if you don't need a lens mount.

Buying one of each is an option... oops