Reading through your posts I really coldn't agree more. All your points about preparation, aquiring management skills etc. are more than valid and most probably many applicants didn't completely step up to them.
But I think the main point is missed. It's the reigning culture that is a huge obstacle. All applying pilots are assessed as future captains. If there is a high upgrade failure rate, then either recruitment did a lousy job, or something happenes during the 4+ years as FOs. My point is the latter.
I observed that many FOs during their early years are first flabergasted by some events, then bewildered and finally almost intimidated.
The company pretends a lot of things, writes beautiful books and in meetings assure us of every assistance and confirm skippers of having all the authority and so forth. But then they see a skipper grilled for letting the FO land (successfully) after an engine failure (BKK), they witnessed a skipper beeing grilled of aborting at high speed when a tire exploded (DXB), they heard about a skipper beeing grilled for landing in Dyarbakir and not where the company would have wished, with an engine failure. They know about the many letters, some even warnings, to skippers for loading fuel when they deem it necessary. They read about the multiple mess-ups by a certain DCP (NRT, DXB, SIM) and must ask themselves why he's still acting PIC AND in charge of upgrade interviews. And I am not even talking about some dismal sackings.
THAT is the actual culture they are witnessing.
There is a huge dicrepancy between what is said and what is done. THAT'S what hinders many FOs to perform adequatly at the interview. They no longer go by what makes aviatic sense, or common sense, they try to accomodate the culture. But, as I mentioned, this is a double edged sword, because the company can apply what is written OR what they deem necessary. It acts in a hugely opportunistic way and this is somewhat difficult to read and live by.
I have heard about an upgrade loft beeing terminated after a few minutes simply because the trainee chose to change runway, due to lenght/crosswind reason, and because the trainer disagreed, he failed him. I can't confirm this, but it would fit the above and greatly increases fears among candidates.
And fear or intimidation, finally the wrong culture, is one of the worst enemies in aviation.
Unfortunately more pilots we encounter than not would strongly confirm this. At a wash-up the ABDCP asked if captains feel pressured by the company in fuel decision making, he was aghast to see two thirds of hands raised.
As long as this culture is upheld and its protagonists can continue nothing can change.