I'm form italy ^_^. Yeah my english is bad but if you understand what i mean it is ok.
Either in standard you can't have only synthetics or you will get bankrupt. You need some income and in anno you will get income from taxes or selling goods in the global market, but the GM is volatile and sometimes you get a lot of income and others you lose money producing and selling goods. So if you want a stable and a big company is better if you don't depend too much from the gm.
Yeah synth are the late game population, Instead of having millions of investors and a bigger and bigger income you sacrifice the income for more population. The workforce for synth is more than double because they have less needs and you save energy and workforce because you will have less buildings.