Correct

Also, most of systems using busybox shouldn't be running Systemd (or any other 'new' init system to be honest)

What about initrd? Most of those use busybox and it's now "recommended" to start systemd there. (Granted, I don't see why anyone would run busybox's syslog - the only component affected by this change - in an initrd.)

If you want an extremely small system, you can put everything you need into the initrd. It's not strictly an initrd then, since it's not really used for bootstrapping a larger system image.

This is the only way I use Linux.

I will use the Linux kernel (although it is not my favorite kernel).

But I am interested very little in GNU userlands and all the idiosyncracies, complexity and politics that comes with them.

uhhhh procd?