I think VSF has worded rather well a critique of your strategy that probably many looking at this tragedy would agree with.
If you add that the a/c had got within 650 yards of the nearest shore at the point where they discarded waypoint A (and about 750 from that fog station, for those interested) and thus appeared to have been in control at least until that point and yet were still at high speed and seemed to make a deliberate turn to the right (into danger) onto a track which they held until 4 secs before impact at which point the a/c appeared to have responded correctly to the control positions found THEN you perhaps should consider approaches other than “airworthiness”.
While some would say it can happen to the best, I personally cannot believe the coincidence of them having a bad day, with their experience and local knowledge in this area, just when they have the particular VIPs on board.
My own analysis of the available data suggests that they were paying particular attention to navigation and that they had a purpose for approaching a known LZ closely.
Whether they were misled by a third party or simply misjudged their approach does not really matter if you are interested in just clearing their names – any such activity would reduce any mistake on their part to an error of judgment if that and together with that such an activity has not been disclosed surely throws out the original verdict of gross negligence.