Maybe the big picture is just too hard to swallow at one go – perhaps you all could apply your knowledge to one significant aspect at a time.
Let's start with engine power:
(from memory)
Luckily (from an analysis perspective that is) the last manouevre was of insufficient duration for the thrust lever demand to have been reacted to by the engine management system and so we know the state of the engines just before impact.
AAIB etc had it that the engines were at matched power settiings and at an “intermediate level”;
Boeing's “Analysis of available data” had it that they had started to slow down on the final leg.
Why don't you all address these two related points?
Do some homework/ask around to clarify what “intermediate” meant – was it about right for coasting in on an approach? – just enough thrust to balance the weight while the speed washed off.
Because if it was and you agree with Boeing's analysis that it was slowing down, then it would seem that the intention was not to maintain the high cruise speed, continuing the route – nor to climb over the Mull. Just from this, the analysis problem is reduced significantly.