Thisis a strange place, for sure...
Yes 5% of the population get 80+% of the income.
Yes, there is more visible wealth, more and better public services (yes, even with their deficiencies) and it is spread out over the country.
IN COMPARISON.
In Mexico or Guatemala or most of Central America, the differences between the capitol city and the rest of the country are huge. Here, not so. In fact, Santiago has a few things not available in Santo Domingo. But the point is that "modern conveniences"are readily available throughout the country. So, okey, you can't get water or electricity in some of the remoter rural areas, BUT you can get a phone!
Santiago has had a paved, international airport for 50 years. POP, Montecristi, Mao, La Romana, Azua all had landing strips a long time ago.
Therefore, it should be rather obvious that there is a reasonably 'comfortable' group of upper middle and upper class folks that do live fairly well, by most European or American or Canadian standards.