You've pretty much nailed the major issues with this scheme.
The cost of living (as an expat) in HKG are astronomical. Rents are breathtakingly high and rising, and although folks who sign up for this so-called "cadet" scheme will eventually be eligible for housing assistance, it's laughable.
S/O's log P2X hours, 1/4 of which count towards a higher licence. No, you cannot log P2 time even when you're in a window seat.
So what's the upside for CX and why are they training people with no time, no connection to HKG and non Chinese?
In three words, the housing allowance. A normal expat here in HKG gets around $65,000 - $200,000 as a monthly allowance. Depending on where you choose to live, it gets you a decent condo or townhouse in a nice area.
Cathay has always been on the lower end of the scale and it's renting less and less of an expat type accommodation.
Although CX pays for your training in it's entirety at a cost of about AUD200K (HKD1.4 million) it takes no math genius to figure out that they've recouped their training costs after a scant 2 years (of no housing to the "lucky" cadet) and it's upside from then on in for CX while the fortunate individual continues to lose significantly over the next 20 years (approximate time to command).
Finally, when command does slide into view, your housing is at a scant HKD24K a month - whilst not a poke in the eye with a sharp stick, is a far cry from the allowances of other expat bankers, engineers and the like.
I won't dispute that it's a decent flying job.
The aircraft are shiny and new, the destinations are interesting, the airline is stable and training is very good. I won't raise the issues of rostering and management, which cloud the bigger issue of remuneration.
So, at the end of the day, you may find yourself in a shiny 777 or A350, winging your way to strange and exotic places...
You just won't have any money.