sysv init scripts are more complicated than just a list of commands to run to start the service. They have start / stop / reload functions and express dependencies. The sysv generator handles all of those. Like this jank: https://github.com/systemd/systemd/blob/08423f6d30f5db045b8a...

So it's not as simple as "Just write a .service with ExecStart=/etc/init.d/whatever start", but it's also not too complicated, especially if someone forks the sysv generator and keeps it working like I said in another comment.

It's generally not; I've never understood the claim that either one is particularly "complicated". You either write a set of sh commands that start the service the way you want to or a unit file that has that shell command plus some random metadata crap about it. Neither of these options are particularly difficult and I've literally never understood why people want to die on either side of this hill.

The pain point was never "generating a textual representation appropriate to the init system"; the problem was always the underlying startup and teardown of the service itself.

Business requirements are never "just don't update this machine", you often have conflicting requirements where one piece of software has one set of requirements and another one has different ones. You often need to update systems to stay compliant with security requirements and those updates are generally non-negotiable.

I'm a fairly cautious sysadmin but I can't say that replacing an init a script with a systemd service is something I'd be afraid of doing