I'm not going to argue the Pros and Cons of the sandpit, I'm not an expert on the conditions there.
It is important however when considering a move to think about the future at cx. The conditions in the FH have been going downhill for 20+ years. This decline shows no sign of slowing down, if anything it has accelerated. The current management denies that people are leaving in any great numbers and think we are adequately remunerated, if not overpaid. This is a clear indication of the company's philosophy, they are entitled to their view and I'm sure they are positioning the company to sell to the highest bidder, presumably Air China. We wish them good luck.
For anyone considering a move this is probably the most important factor. However bad the sandpit or other options are, in the long term leaving is probably the better option. Remaining at CX is probably a very bad option indeed if you have more than 12 years or more to go. As the past shows, things will only get worse.