Moreover, for example, I can update my running containers based on Fedora 23 without restarting container, by issuing "dnf update", which will download updated package from local server, which is much faster that to build container, publish it to hub, download it back, restart container (even when only static files are changed).
Faster is objective, and in most cases correct. Glibc has a lot mor optimization over the years. Better is subjective and completely depends on your use case:
http://www.etalabs.net/compare_libcs.html
Similar point to systemd, it is kind of misleading to say that it's faster, it is parallel and event driven, which definitely makes it's end to end time shorter on parallel hardware. And again better is subjective, it's so much more complex that it might not always be the right choice.
Also, why use systemd inside a container at all? There's just one process in there usually.
[vlisivka@apollo5 docker-centos7-systemd-unpriv]$ ./enter.sh
[root@e3c3dd7539ad /]# ps ax
PID TTY STAT TIME COMMAND
1 ? Ss 0:00 /usr/lib/systemd/systemd
71 ? Ss 0:00 /usr/lib/systemd/systemd-journald
74 ? Ss 0:00 bash
92 ? R+ 0:00 ps ax
Thanks for the information.