With 16.04 I get core lockups (Intel microcode) and cannot switch out of X with Ctrl-Alt-F1.
NetworkManager no longer connects the mobile surfstick, so I do it manually now with pppd.
I can't claim that I had a specific problem with systemd, but I never had an issue with SysVinit either.
The overall trend however is that Linux distros accumulate crapware by RedHat's NIH developers. I'm not surprised that NetworkManager is also by RedHat.
Apparently not -- netplan is ubuntu originated. They don't do themselves any favours.
For networking I suggest looking at ConnMan. It has a somewhat unintuitive UI, but it is lightweight, fast, and I have yet to find a wireless network that it will not let me connect to.
You can't switch users within x either, it's been broken since at least 14.04 (according to an old close bug report I found). It works the first time but on subsequent tries you just get the lock screen.
The bug report was closed after several years of nothing.
Since some time switching VTs resets all hardware accelerated applications (i.e. crashes them).
Since some time unlocking the graphical session is randomly broken and requires loginctl session-unlock from another VT (which then promptly triggers bug 2).
These things keep coming and going... it's not even Linux-specific. Stuff just breaks all the time and you shrug and move along, hoping that maybe someday it's fixed. For most of these I wouldn't even know who should receive a bug report. Maybe it's the graphical login, maybe the compositor, maybe mesa, maybe a kernel driver, maybe systemd, maybe maybe...
You could try Ctrl-Alt-F3, F4, etc to get a login terminal.
Not all SysvInit implementations were equal, which was an issue in itself.