You haven't requested systemd, you started a user scope, and haven't started a service for what you need.
POSIX is nice, but rather lacking in certain aspects, such as security anf administration-friendliness. cgroups help with both, but people have to understand them and use them well.
Handling and ignoring SIGHUP is the explicit way to indicate that a program should not be terminated. That systemd invented a new category and then ex post facto declared that everybody else was wrong for not using it is ridiculous. Systemd changing behavior such that I must "Simon says nohup" is completely asinine.
POSIX is nice, but rather lacking in certain aspects, such as security anf administration-friendliness. cgroups help with both, but people have to understand them and use them well.