There may indeed have been a plan to reduce expat numbers, before VJ and Bamboo started plundering all the local pilots, but the fact is that right now the Vietnamese captains and high time FOs are leaving faster than they can upgrade them. They can’t get more locals, so their option is either to hire more expats, or park aircraft.
A330 was a special case because the fleet was getting finished. We (the FOs) were all offered the A350 RHS but most of us chose not to take it, because we had offers from several other companies to go and take quick commands elsewhere.
There are certainly issues of concern here, but job security isn’t one of them, for anybody except Kimono anyway ��