I doubt that Leica goes through an evaluation of the rangefinder mechanism when going through the initial product design phase for a new camera project. I also doubt most people buying a rangefinder camera go through the process as well. I see many buying new Leica equipment and used rangefinder equipment based on brand and product recognition. Many long-time Rangefinder shooters know and effectively use the advantages of a Rangefinder camera. Recent articles to “time to abandon the Rangefinder” could have been written 60 years ago when SLRs were popular. Here we are in the 2020s and the major manufacturers are ending development of new SLRs and Leica is bringing out new Digital and Film cameras using Rangefinders.
Advantages of Optical Viewfinder/Rangefinder:
You can see things outside the frame. This makes it easier to compose the shot. This also makes it easier to follow a moving subject.
The Viewfinder does not black out when the shutter is released. This makes it easier to make a sequence of shots, For moving subjects, makes it easier to pan and focus.
Optical viewfinders are bright. If there is enough light for your eye to see it, your eye will see about the same level of brightness through the viewfinder. The RF patch is at least as bright.
Lower Latency with all-mechanical shutters. The shutter is closed while viewing and focusing. All-Electronic shutters are also low latency, but have problems with some artificial lighting.
No power draw. The viewing and focus mechanism is opto-mechanical and does not require battery power.
No latency when viewing the image. EVF introduces "Digital Delay" between the sensor acquiring the image and the image being displayed. Higher resolution EVF requires a higher data rate and faster processing, which increases power draw.
Disadvantages:
Requires Precise mechanical calibration between the Camera body and the lens. This is expensive to implement. Maintaining precise calibration is difficult.
Not “What you see is what you get”. The photographer’s view is not through the lens.
Precise agreement between the Rangefinder and Lens varies depending on lens aperture and filter used. “Focus shift” due to spherical aberration and chromatic aberration cause disagreement between the rangefinder and lens. Apochromatic and Aspherical lenses that minimize these problems are very expensive. Attempting to correct the issues mechanically would be very complex, and have not been done.
Most manufacturers are switching to EVF designs that use the Sensor for viewing. This is a direct replacement for SLR viewfinders. EVF viewfinders with 3.7Mdot range and higher and with focus assist are a direct replacement for SLR viewfinders. The main disadvantage is power draw when compared to an SLR. The "age-old" comparisons made between SLR and RF still hold true comparing EVF and RF.
Maximum "practical" focal length is 135mm.
Requires add-on External Viewfinders for focal lengths longer or shorter than supported by the viewfinder built into the camera.
Requires Eyepiece "Magnifiers" to accurately focus longer focal length lenses from the 85mm range through to the 135mm range used wide-open. Not required when stopped down to F5.6 or so. The same magnifiers are useful for 50mm lenses faster than F1.4 used wide-open.
Maximum Practical minimum focus is about 2feet, 0.7m. "Absolute Kludge" devices allow close-up work.