I suspect it’s very high 90s of percent.
And yet, the bigger a software company gets, the more labyrinthine its systems get. Ask any software or IT engineer who was at, say, Amazon, Facebook, or Google, as the company grew from serving a few hundred thousand customers to hundreds of millions of customers.
Similarly, the bigger a country is, the more labyrinthine its systems are (tax, legal, regulatory, etc.). Large distributed systems tend to be come very complex, even though no one wants them to be. There are always many competing interests negotiating with each other and reaching compromises that no one likes.
It's not the number of customers so much as the number of diverse things they do. Ditto for a country's taxes. I expect the Faroe islands' industry is fairly limited compared to the US, so they may not need as many exemptions, tax credits, deductions, etc. No doubt there's still considerable room for streamlining though.
2. Taxes should only grow in relation to the growth of identifiable government needs. There is no reason that the government ought to grow linearly in proportion to the net wealth of the country.
For simplicity sake, a 10% tax on income would scale infinitely, no matter how big an economy grows (I’m not arguing in favor of this tax).
But the point of the article, in my opinion, is that US has a large problem, costing tax payers an estimated 40 billion in labor figuring out their taxes, where other countries have almost automated the entire process.
I think there is something to be learned from there, as most people would agree that the US tax system is a mess.