Two things have been left out of this conversation, both related to competency.
Large MNC's might be having an easier time with EP's than other companies, but those other companies are the ones that support the big MNC on a contract basis.
Take IT support, for example. The pay is low for an onsite support guy because the MNC's are so chickenshit cheap in their contract negotiations.
It is really hard to find a Singaporean who will work for that money, has sufficient skills, and is willing to do the physical things associated with onsite support... pulling cables, crawling around on the floor or in the ceiling, assembling and disassembling PC's, changing laser toner... all those things.
The Singaporeans that are willing to work for that sum of money are marginally, if at all, qualified to do the work. Poor reading comprehension. Lack of problem solving skills. Not much in the way of social skills, either.
I've seen IT service companies lose their techs because the EP's and SPasses they had were not renewed. They are not getting the same quality of local talent. Even with training, user complaints go up.
And on the other end, why is it that MNC's are bringing in expats at the top managerial levels? It is expensive to do so. It is about competency and leadership. Certainly there are lots of competent and qualified Singaporeans... but there are also lots who view management and leadership roles in a way that reduces their effectiveness... unwillingness to take risk, unwillingness to make hard decisions, over authoritative management style, a lack of understanding of what management is all about, and an uninspiring leadership persona. I've seen lots of situations where problems fester and fester because no one wants to own the issue and get it fixed. It's always someone else's problem.
All the local hiring policies in the world change neither of these circumstances.