The sudden nature of the accident would point to either a CFIT or a Mechanical break up. What about fuel? It left heavy and was needing a refuel shortly before the crash, someone could work out the burn rate between the time periods and rule that one out surely? CFIT? What could go wrong for the aircraft to fly itself into the water? Mechanical break up? MGB? TGB?
Just my 2 cents worth
You made your point well but then went into random speculation which helps no-one