No just any pilot or engineer can just walk in the ATSB's front door and start generating suitable reports, it takes years of experience - even for highly experienced pilots and engineers
Interesting observation re the vast experience needed nowadays to write a report. I am sure it has changed now in the RAAF but during my time there in another era, accident investigations were over and done with within one month to three months.
Having said that, there was no such position as a professional accident investigator in the RAAF. A prang occurred and you would be allotted to investigate what caused it. It was called a Court of Inquiry. As a General Duties RAAF pilot it was expected you would fall back on your experience of flying that aircraft type and common sense. Suitable resources were at your disposal. Of course there were no CVR or FDR's then, so you and your team would scratch your heads and do the best you could.
One thing for sure. There was no going on recreation leave causing long periods of inactivity during the investigation and I don't recall the legal eagles agonising over the wording of the report to cover possible future litigation. In other words Courts of Inquiry didn't stuff around.