If you can attract a significant slice of the world's wealth and somehow funnel just 1% into the local economy, that can be enough to provide generous services for a 6-digit population. But it obviously doesn't work for anything larger. My example of Ireland, above, is probably just on the threshold. And the model only worked for them because they also have a well-educated and english-speaking population, making it attractive for actual operations to be located in Dublin.
The problem is, obviously, that this is an international zero-sum game. The US, Russia, and most EU countries provide all the infrastructure that allowed their citizen to earn the money, but the money leaves those countries as soon as the tax-man rings.
Which is why the last decade has seen an assault on tax havens: Switzerland's bank secrecy laws have already been neutered, Panama has lost most trust with the recent leaks, and Ireland is forced to play nice by the EU.
It's highly likely that oligarchs will soon run out of such locales, because it's becoming increasingly difficult to maintain both ingredients necessary for a tax haven: you need not only low taxation, but also robust rule-of-law. Those two goals come into conflict once the first is used to brand you an international pariah.