See my comment below. These tools are fundamentally broken for this use case and have never provided the functionality needed. Bash scripts are not a process manager and it is incredibly wrong to try and make it work like one.

I've already been in a forest of bash scripts and I would not go back there again. I have no comment on systemd's implementation but the implementation you're talking about is also incorrect. It has never been safe to kill random processes using a bash script running in the background, on most Unixes (and Linux) it is 100% impossible to do that without race conditions due to the limitations of procfs. Doing "ps | grep" and "killall" is a footgun. You would need to implement this in C for it to have a chance of being safe at all, and even then, you would need to rely on system-specific functionality because there is no portable way in POSIX to actually do this.