* Michael Biebl <biebl@debian.org> [2021-07-09 12:29]:
That tightly versioned dependency doesn't help unfortunately. There is
still a time window between the new libsystemd-shared and the new
systemd being unpacked.
There's also a time window between files in /usr/bin and files in
/usr/lib being replaced.
If you reboot your system with an unfinished/interrupted upgrade,
you cannot assume a consistent or bootable state. Packaging all
stuff in the same package *may* reduce the above time window
somewhat, but it will not eliminate the underlying problem, so it is
a non-solution.
There may be other reasons to object Helmut's proposal, but this is
not it.