The major issue with long term SOs is that it different sitting in the front seat, despite all the work that you can see from the back. Many diligent and high quality people will still probably struggle a little because of the lack of exposure to ops below 20k in the front seat for x number of years. It used to be when you would get the SO out at 5000 that if they could get you to 20 miles 250kts at 5000 then job done. (Add a few miles for 330) If they could do that consistently then FO training became about 5k down as opposed to know where it is about TOD down. The 20k limit does absolutely nothing to help advance or keep any semblance of skill. The SOs also lack any familiarity with domestic ops which makes up most of their training (small stuff that takes away brain space like co-ordinatior in Sydney, COBT and the different requirements for it in each port) I’m not sure about sector numbers compared to the 737 anymore but it used to be significantly different along with fact that 330 trainers seem to sing from sdifferent song sheets from each other more so than the 737.(less consistency of message than the 737 which is what trainees need more of)
Couple that with a few idiosyracies of the 330. Such as the fact that 330 is one of the slicker jets out there and an FMS decent path that pretty much guarantees you are high on the ideal profile (ie the FMS path is crap without work arounds such as lower than planned speed at GS intercept) Or the tendency if your aimpoint is at the end of 1000’ markers as many teach the chance of landing short is dramatically increased which the sim doesn’t adequately prepare you for. (Landing short is a big no no in training) it is probably little wonder why some struggle. Laziness on removal of the golden handcuffs also possibly plays a part. It also must be remembered that people generally do not fail for one reason. A pattern generally develops.