The idea that incoming phone calls should be relegated to simple banners is beyond absurd, and I'm sure brings with it all kinds of legal and social impact concerns for Apple. This isn't just software.
And no, making it "an option" is not the answer for bad ideas.
There is a new feature iOS 13 that lets you silence all unknown calls. That should be more than enough to address this strange concern of not wanting to answer calls.
No, you are wrong on that one. It is not enough, what if I want to quickly swipe away the call from Sancha, also my wife doesn’t see it?
I think you area way off the mark on the "legal" aspect of it, there is no law that says an incoming call has to take the full screen. Are you serious, and actually believe that to be even remotely possible? If you live in some strange nation, or place that exerts unnecessary control over its people, like deciding how loud you want your earphones to be, or decide that you shouldn’t be allowed to use Google, then maybe....
I challenge you to show me a law from ANY land, from the Land of the Free.....to the land behind an iron or red curtain...Just show me one, that says you have to have a full screen display for an incoming call on a phone, or any device.
Social impact concerns, as you can see clearly from this post they Cleary do have a social impact concern. That is proven by the fact that we are socializing about it, and users (how many users, who knows) would like change...
The ability to allow banner notifications, for "less intrusive" call notifications, while using other aspects of the phone, is in my opinion an excellent solution.
I will openly admit, I am NOT a programmer, I am NOT a software developer by any means. I am an end user of Apple products going back to my first one, an Apple IIGS...I certainly can not testify to the ease, ability, or inability to make those changes happen, but as an end user, it is not problem, I want what I want.
As far as being possible technically or not, the poor solution on my Samsung Galaxy S(something), is very awkward and poorly implemented. I do have faith that in my 30+ years of being an Apple customer, that they can do better than Google or Samsung.