Engineering analyses, as diligent and well founded with appropriate assumptions as they may be, will never explain the potential motives and actions of individuals unseen by the rest of us.
I don't believe that the ATSB analysis and investigation is likely to conclude along the lines of deliberate action by the pilot/s in control at the time of the incident to ditch the aircraft for other than emergency reasons. That sort of conclusion moves into potential criminal intent, which is a matter for police/coronial authorities to adjudicate upon.
The technical authorities, like the ATSB, is where the expert analysis investigation rules out other possible/reasonable reasons in the technical/operational realm.
So it seems the aircraft is not likely to have descended in a controlled manner as analysis/inspection of some of the flight control system components recovered do not support the 'controlled descent' hypothesis.
As disturbing as it sounds, I personally believe, and have for a long time, that the aircraft's descent was very rapid and very steep and it entered the water in that attitude and dove very deep. Only the 'flimsiest' of secondary and tertiary external structures would have been at risk of breaking off in that sort of instance, where the vehicle enters the water in the most 'streamlined' orientation possible. And this, I propose, is what we appear to have seen with the debris that's been recovered and the state/condition that it is in.
On a relatedasdie,, aerodynamics and fluid dynamics are two very closely related diciplines and the study and design of vehicles operating in those environments are very similar. In fact we treat the air that aircraft fly in very much like a fluid with similar properties and characteristics.