You can still have your wonderful script but in the case of systemd, you delegate the execution lifecycle of that script to a unit, which, IMHO, is a great abstraction compared to the mess of having to deal with the status of the service from the script itself. You simply throw the unit file into directory, then enable it. Your script does its thing, systemd deals with when to run it, in which runlevel etc
About the logs, yes, plain text files, commands and pipes are great, but journalctl is really great too. It is powefull and includes everything you might need to inspect logs with accuracy in the same tool.
Just to clarify: I'm not a fanboy, I'm just pragmatic.