It is extremely rare, almost not believable, that CX airport control will not be releasing seats to your family if there were indeed space available in business class cabin. At that point, airport team takes control on seat release/redemption and once they are ok to release then you just need to call the CX hotline to change the ticket and pay for the new taxes. I did it a few times myself and I was with miles redemption tickets. Essentially I was on 'standby' and trying to fly out on an earlier flight or a change of cabin on the same flight. I am also a CX Diamond member.
Anyway, if your case is true that it is simply ridiculous!

Also I am not defending the ISM, but the cabin crew have no clue what type of tickets one purchased. Whether they are revenue or redemption tickets, full or discounted fares, it makes no difference to them. So she was only doing her job to inform you that swapping seat with a child is not allowed. Cabin crew only know which passengers have been upgraded by airport control (involuntary upgrade) due to cabin oversold.

what exactly is “Asia Miles Diamond Member”?

You lost me at "top tier member of Asia Miles"

Sorry but I laughed non stop after "top tier asia miles member", and coughed non stopped at "Asia miles diamond member".
I am saving this as a pdf in case the thread disappeared for some reasons in the future.

And of course, if CX now try to ramp-up schedules (assuming they can find sufficient Captains & First Officers), cabin crew will be further stretched. Once again, lost a lot of seniors and numbers appear to be spread very thinly. Hence reduced service based on my recent experiences: (i) no drinks service in Y other than at same time as serving dinner; (ii) cabin crew basically disappear whereas pre-Covid they'd still do walkabouts; (iii) breakfast being a derisory and barely edible chicken sandwich.

Yes, maybe "first world problems", but when CX continues to charge premium fares as compared to other full-service carriers, service delivery has got to match.

So, I'm more-than-half-expecting service quality to further slip during the course of this year.

My status updated, please check.

Figure I should be more humble with mines.

Yes indeed, it’s a real worry to which can be added the issue of senior pilot staff to which you refer. I assume CX hasn’t got a chance as long as it retains the remuneration approach largely as implemented during COVID. I’ve been a loyal customer throughout and CX has been good to me over the years. But I won’t hesitate to walk away if core safety standards are compromised because of inexperienced, exhausted or utterly demotivated cockpit crew.

The only experience i have with these kind of ticketing scenario is that the "taxes" paid for Adult are more expensive than kids tickets. I learned this once (cannot remember which airline). So they won't allow us to change. I.e. in your case 1 adult + 1 kid in J is cheaper in taxes than 2 adults in J. So in your case I wasn't allowed to swap seats. So after that I just paid for adult tickets even though they were kids (I just declare a wrong birth year if asked). Never had an issue after that.

I can’t be bothered to read the OP’s mile long rant, but from the first few paragraphs, it seems they got the exact seats they paid for?

I hardly think "core safety" will be compromised. If it were you might hear more leaks of pilots pressured to secretly go over 900 hours or something. Instead, hitting that limit is an issue. The "service slips" we hear about most are instead the level of thing like "I wasn't offered a refill on my brandy within ten minutes of dinner service." Would worry far more about safety on any airline flying the Boeing 737s that haven't been grounded.

Perhaps I'm missing a pertinent fact, how would OP redeem business class and premium economy at "the same number of miles"?

I have been a long-time visitor to this forum and sadly am feel very disappointed by some of the responses in this particular thread. Irrespective of whether the OP was reasonable or not with his actions/expectations, the sharing of his experience is useful data for other travelers. It does not take a great deal of mental extrapolation or empathy to work out what the OP meant by "top-tier member of asia miles" is what we would normally call CX DM, he has a post count of 3 which suggests to me he normally has better things to do with his time than lurking on these forums and learn the lingos of FFPs. How is the pedantry adding to the discussion? Why not just focus on the subject of the inquiry?

If the OP was an unreasonable person he would probably have demanded that his children be sat in J with him and his wife, something that I am sure many of the regular DMs here may hope/expect if they were in the same position.

Regarding "the same number of miles" argument, I believe what the OP meant is that adult and child (AM) prices are the same, hence swapping seats would not result in an adult occupying a cheaper-priced child seat.

Of course, the ISM had all the rights to demand pax remain in their own assigned seat, but taking the story at its face value, I think the ISM could have acted with more flexibility and empathetically. It would have cost CX nothing (not even an extra bottle of water) but added plenty of goodwill for this top-tier member of their Aisa Miles program, Sorry it should be "Top tier member of Cathay".

[mod edit]

Which was precisly what OP tried to from the beginning to the end. And failed.

You make some very good points about not making fun of those who lack the proper vernacular or jargon. I'm often at a loss myself. For example, it took me a bit to figure out what ISM might be. Eventually this is clear through context but that's not so easy for everyone. So let's be kind to others.

However, what I really take issue with (and maybe this ticked other users off as well) is this fatalist attitude some OPs have on this forum and immediately call doom upon the airline. Just because they had a disappointing experience, doesn't mean they have to be so dramatic about it. And to be honest, if he really is a diamond member, he should know what is and isn't allowed.

Also, like so many other things in RichMegaCity, the CX's "travelling with children rule" is so ambiguous.
These 2 rules seem to contradict one another, because how can you be accompanied by your parents at all times if you're not sitting in the same cabin?