>>> But more importantly, current screen technology requires the driver to focus on the surface of the screen itself, which is mere feet away from their eyes. This is a large change in focal distance from looking at the road ahead.
If you’re over the age of 40 or so, it takes time, a few hundred milliseconds at least, to refocus your gaze distance. A screen is near. When driving, you’re looking far. A mirror is something to glance at.
I test-drove a Polestar with a screen for a rear-vision mirror (and no actual rear window) and it was completely undrivable for me. It takes longer for my eyes to refocus on the near distance than I feel comfortable removing my gaze from the road ahead. I turned around after 10 minutes and returned it to the lot.
Also, this conversation is about backing up and parking (read what I said). When backing up you are mostly looking backwards only, so the focal length adjustment point is moot. Even if you have to switch to looking forwards, this is at low speeds / standing still, so it doesn't make a difference.
I'll restate my point with emphasis because you seem to not have read it: Cameras are infinitely more useful for backing up and parking.
Sometimes I sit in a coffee shop and very often see people just using their side mirrors (no rear cam, not looking back) ... scary.
I say this as someone who learned to drive and drove for a long time with no cameras. People saying this are just usually just used to mirrors and never bothered to take the time to learn to switch to the cameras for backwards maneuvering, or their cars just are not equiped with the latest tech.
Using the rear-view cam in this context is definitely a lot safer (esp for kids!), though you really should also look around as well, the side mirrors are more for driving, not parking-lot type situations, and have a really limited field of view.
What I meant was: people backing up just using their side/rear mirrors are scary. They don't have good spatial awareness of what's around them. A rear-view cam for them adds a whole lot of safety though.