A good doorbell camera will have a wide view that is the point to see the entire surrounding area including your packages etc... A narrow lens doorbell would be foolish... Particularly since everyone has different mounting positions.... You will want a good front camera anyways.. if you believe it's so easy to develop go for it yourself... Axis has a good doorbell it's 800 bucks....
I fully understand that for many people on here, doorbell cameras are 2nd cameras that only supplement CCTV. But, for others who don't have / can't afford CCTV, the doorbell camera might be the only the protection they can put in place. In the UK atm, the manufacturers are staring to push doorbell cameras with both Ring and from memory Nest pushing doorbell cams via TV adverts, and Nest pushing a small wifi camera for the house / garden. This year is the 1st time they've been TV advertised that I've seen. It seems logical that if these are going to be the only cameras for many, to have the best image quality.
As for developing my own, again I take your point. But how is a doorbell camera so far from a cam such as a Mobius (I choose that as an example I know is quite easy to play around with as the internals can all be bought separately as spares and it's more sport camera with dashcam ability that dedicated dashcam)? The Maxi for example has wifi connectivity, 2.7K resolution, a great lens choice (2 angles), recording to SD although no doubt with Wifi and a good signal it might be possible I would have though to stream and record to a device, and it costs around $80 retail + a few $ for a capacitor option. Surely given it's functions the only real difference between this and a doorbell camera is the waterproof casing and the software for 3rd party device recording. They both stream, the Maxi at a much higher bit rate because it deals with lots of movement, but that's nothing more than a firmware adjustment, they both can record continuously, neither has a battery and can be powered by hardwire (the Mobius when fitted with the supercap and currently via mini usb port although I'm sure a 2 wire bell connection is only a few bits of solder away), they both have mics, admittedly the Mobius doesn't have a speaker to allow you to talk back - a function of many door bell cameras. However, the latter feature apart, there's not really that much difference on the surface between a small multi-purpose action cameras and a doorbell camera. Of course, for a doorbell function, a wireless door push would also needed to be added and the end camera combination is not going to be as small as the latest Rings, but function vs form.
I've seen some really bad, fisheyed-to-the-max images from doorbell cams. Sure, they could be used for ID purposes, but the distortion created by the lens was significant, and it certainly didn't improve the odds of identifying the Bad Man.
That's exactly my point. When I switched over lenses on my Mobius, I noticed the narrower angle was significantly better for resolution yet still gave me more than enough fov in my car. The Mobius uses a high quality lens for both so distortion was never an issue, but simply having more pixel density really helped identification.
I agree with 2.7k you're never going to get distance recognition with a doorbell camera, but the whole point of them is protect you against someone who comes up to or comes up close to your door. When You look at some of the current crop of doorbell cams, the ID ability of them is really poor even where this is the case.