My take, and let's reiterate that we're talking about USER systems: Up until 1954, when the M3 appeared, Contax was 'way ahead of Leica in technological sophistication (combined range/viewfinder and non-rotation shutter speed dial) as well as breadth and quality of lens line. Many users preferred Leica for its more comfortable handling and better real-world reliability; however, by 1950 the smart play for Barnack fans would have been to buy a Canon, which had similar handling and quality plus the operational advantage of a combined range/viewfinder with switchable magnification. Likewise, Contax admirers could have gotten the same overall handling plus the less complex Leica-type shutter by opting for a Nikon S, although they would have to give up the single shutter-speed dial.
By modern usability standards, the main drawback to all of these — and the reason I can't take any of them seriously as user cameras today — was their dinky, squinty, ornery viewfinder eyepieces... necessary to keep the user's eye centered behind their simple Galilean viewfinders, but infuriating by today's standards. Slooooow operation enforced by knob wind and rewind also was par for the course for the era, but harder to accept today if you're serious about taking pictures. Inconvenient, or even absent, flash-sync arrangements are less mission-critical, but still annoying if you want to slip a strobe onto your camera occasionally.
With the M3 of 1954, Leitz obliterated (almost) all of these headaches and went from last to first place in usability. The M3 had a large, comfortable eyepiece thanks to its system of projected viewfinder frames; a rapid film-advance lever; all shutter speeds on a single dial that didn't rotate as the shutter fired (hence no risk of hanging up on an errant finger) and straightforward flash sync. (The only place they dropped the ball was in retaining knob rewind, which spawned generations of cottage-industry aftermarket solutions until they got back on track... 13 years later!!!... with the crank-rewind M4 of 1967.)
Of the rest of the system-rangefinder Big Four, two rose quickly to the challenge. By late 1954 Nikon had rolled out the S2, with a bigger, more comfortable reflected-frame viewfinder — not as flexible or as easy to use as the M3's projected-frame finder, but still a huge advance over the dinky Nikon S finder. The S2 also had both lever advance and crank rewind for much faster operation, and a PC flash contact with X sync. Its main usability drawback by modern standards was its system of separate, rotating fast and slow shutter speed dials, which are much more likely to confuse the modern film newcomer than the M3's single dial. Nikon rectified this by 1957 with the SP model, which filled out the full slate of modern conveniences by adding single-dial shutter speed control and easier-to-see projected finder frames.
Canon wandered a bit longer through several transitional models until 1958, when it brought out its VI and P models, all with reflected framelines, lever (or trigger) advance and crank rewind, single shutter speed dials, and strobe-friendly flash sync. Projected finder framelines came in with the big-selling model 7 of 1961.
So by 1961 three of the Big Four had all the convenience features we expect of a modern RF camera: a large finder eyepiece with projected framelines, rapid advance lever and crank rewind (aftermarket on the Leicas), single-dial shutter speed control, and strobe-friendly flash sync.
Meanwhile, though, Zeiss had been sitting on its Stuttgart backside, and by the time it went out of production the Contax STILL had a tiny, squinty finder eyepiece and knob advance and rewind, although it had had single-dial shutter speeds all along and the color-dial model added a PC flash contact with strobe sync.
By these standards I would say the Contax NEVER made it into the modern era of usability — beautifully crafted, yes, and rewarding to use for the enthusiast, but a little too quaint and frustrating for the contemporary user who's more interested in photography than in cameras.
Again, remember we're talking about modern standards of usability... by classical standards, I love the darn old things...