> initramfs, that is a compressed image that includes everything the system needs to boot
Not always (raise your hand if you've had an unbootable system due to a broken or insufficient initrd).
In retrospect, the whole concept of the initrd seems like an enormous kludge that was thrown together temporarily and became the permanent solution.
> initrd seems like an enormous kludge that was thrown together temporarily and became the permanent solution.
Eh, kinda. That's where "essential" .ko modules are packed into - those that system would fail to boot without.
Alternative is to compile them into kernel as built-ins, but from distro maintainers' perspective, that means including way too many modules, most of which will remain unused.
If you're compiling your own kernel, that's a different story, often you can do without initrd just fine.
It's a lot simpler to merge them in a directory that can be mounted across multiple machines than have four separate mountpoints.
Nearly every shell script starts with "#!/bin/sh", so you can't drop /bin. Similarly, nearly every python script starts with "#!/usr/bin/env python", so you can't drop /usr/bin.
Hence symlink.