The net migration stats have nothing to do with ease of getting citizenship. It just calculates the number of people who wants to get in vs those who want to get out. Currently, 260% more people want to get into Singapore compared to those that want to leave it, making it the number 1 migration target in the world.
It takes at least 2 years to get Singapore citizenship
after you get permanent residence. It normally takes years for a S/EP pass holder to get PR. So the average S/EP pass holder needs at least 4-5 years to get citizenship. (
http://www.ica.gov.sg/page.aspx?pageid=132&secid=130#eligibility )
Even if you marry a Singaporean, you normally get a LTVSP for 2 years. After 2 years, you get PR. After 2 years of PR, you are eligible to apply for citizenship via registration. So the marriage route takes 6 years.
In Jamaica, St Lucia, Barbardos, it is instant citizenship for spouses for citizens. In S.Korea, it is 2 years to citizenship for spouses. In America and Britain, it is 5 years.
Contrary to what you assert, you can get Thai citizenship after 5 years though Philippino citizenship takes longer, like 10-20 years.
Hope that helps.