You want a really low tax rate? Look to business and hard assets, like real estate and commodities. In many countries, like the U.S., expenses incurred to earn interest income, retirement income and wage income are only partially deductible or not at all deductible. Yet expenses incurred to earn income from businesses, investment real estate and oil and gas are fully deductible.
Why is this? Because these assets represent primary wealth. Primary wealth is wealth that comes from the initial asset. This includes wealth that comes from the ground (oil and gas and agriculture), wealth that comes directly from a building that is used to build more wealth (commercial buildings) or to house workers (residential rentals), and wealth that come from businesses that produce jobs for millions of people.
Expenses incurred to produce secondary wealth are less desirable to the government, so they are less deductible. Secondary wealth includes wealth that is one step removed from primary wealth. This includes private offerings, hedge funds and private equity. Those who invest in secondary wealth are often limited in the expenses they can deduct and when they can deduct those expenses.