DarkMetatron

The structure is changing, many distributions already are merging more and more of the duplicated subdirectories in /usr/ with the counterparts in / but it takes time to complete that and at the moment those subdirectories are often still there but as symlinks to be compatible with older software (and sysadmins).

Yes, that is true. I was speaking in the context of very early Unix/Linux before initrd was a thing.

And I still don't know what's the point in separating /bin, /sbin, /usr/bin and /usr/sbin.

This goes back to the olden days when disk space was measured in kilo and megabytes. /sbin/ and /usr/sbin have the files needed to start a bare bone Unix/Linux system, so that you could boot from a 800kb floppy and mount all other directories via network or other storage devices as needed.

It gets even more complicated nowadays because most DE will mount removable drives somewhere in folders like /run/$USER/

Mostly historical reasons, /home was often a network mounted directory, but /root must be local.

And only regular users have their home in /home

Well then the answer will most likely be: because they can and want to do it.

Maybe because that person uses systemd everywhere else and just doesn't want the overhead of maintaining two different init systems.

There is no indication that anyone will be pruning systemd from distros in the near or far future. Systemd is here to stay and if anything it will only spread into more and more places as can be seen with projects like this.

Could be a cover to easy access a ssd slot and RAM banks.

Yeah, they should have used the names in alphabetical order, like Ubuntu with their codenames.

As a disclaimer: I really like Wayland and use it as my daily driver for months now with KDE/Proton.

Now my answer, based on my best knowledge:

Because there is no real Wayland to implement, the base Wayland protocols are extremely bare bone and most of the heavy lifting is done by all the different wayland compositors like hyprland, plasma, Mutter, weston, wlroots, gamescope so as a developer you don't have one target to program against (X11) but lots of different wayland implementations and those are not always doing things the same way or providing the identical interfaces/API or have the same level of features.

On my system is at least one wayland only program that works absolutely fine when started in a wlroots environment but crashes (reproduceable on different systems) with a segmentation fault in Mutter or Plasma.

I use arch on my servers. It is the distro I am most used too, because I use it also as my daily driver.