OK thanks for clarifying. I understand your point better where I missed it before.
Still, I think there's some sense in being able to control your editor without moving your fingers from the home row, and learning unintuitive-but-powerful tools for a significant subset of users. If you spend eight hours a day most days using a text editor, then criteria like [ease-of-use to new-comers] ranks a lot lower than others, such as sheer power.
Regarding user expectations - the OS doesn't train users to use the arrows. Bash does, and only when it's in emacs mode. If you sat down at a Solaris console, often ksh would be the default prompt and arrows wouldn't work. Vi interaction would. (You can configure bash to work like this - this is how I work. set -o vi)
I realise that from the perspective of a new user, what I've said above that would feel like an insultingly meaningless technicality. That kind of thing used to drive me around the bend.
I strongly agree with your conclusion,
Anytime you talk about how UNIX-like systems have
evolved, there's a danger of falling into the trap of
hailing historical cruft as "misunderstood features."
But at the end of the day, it's still just historical
cruft.
I loathe "it should be that way because it is that way" justifications, or arguments that defend appalling design with "oh you just need to get comfortable with how it works".