The NTSB does a better job of investigating GA accidents now than they did in previous decades, but not nearly as well as commercial airliner accidents, train accidents, or bus accidents. They just don't commit (or have) the money and resources necessary for an in-depth investigation of GA accidents. Some other country's accident investigation organizations often do a good job on GA accidents (Canada and Australia come to mind).
But it's to Mr. Nixon's credit (and the NTSB) that corrections will be made. My wife and I were in a partnership with a friend (Dave) and his wife in a Rolladen-Schneider LS1-f sailplane
. In October 1978, my partner was flying the sailplane and was involved in a midair collision with a Piper Saratoga on a CAVU day. Dave and 4 people in the Saratoga perished in the accident. The NTSB did a quick investigation, and there were several factual errors in the final report. As co-owner of the sailplane, I pointed these out to the single investigator assigned to the accident. He was adamant that there were no errors and would not change a thing. One that sticks in my mind: The investigator misidentified the Variometer
, which is a sensitive rate-of-climb indicator, with a "g"-meter. I explained what a Variometer was, and told him the there was no "g"-meter installed in the sailplane. He was adamant that he knew what a "g'-meter looked like and that (Variometer) was a "g"-meter! I should note that in this case the factual errors did not affect the Probable Cause finding (i.e., The pilots of both aircraft failed to see and avoid each other.)
So I'm always a little bit skeptical of NTSB GA accident reports, but not so much of commercial airline accident reports, which are usually well investigated.