I didn't see your comment until today. I didn't read the article in full before, but did today.
The stats it gives about philanthropy are not helpful, as they just talk about relative growth, but don't say how much is given as a percentage of total wealth. People like Bill Gates are a net good for society because they look at effective altruism, but the people having fancy concert halls named after them in small towns are not helping. I think the article makes a good case but I'd want to see more detail about % of wealth given to charity by billionaires, as well as more on what charities - e.g. effective altruism vs supporting local church.
I think I'd like to see higher tax bands. In many countries, the tax bands just stop at around 40% or so, and it's the same 40% if you are earning $0.5 million or $500 billion. In some cases, the rich pay lower than 40% because they structure their earnings in different ways rather than as a salary.
I think I'd like to see something like e.g.
50% above $200,000
60% above $2 million
70% above $100 million
80% above $1 billion
And make sure it covers all personal wealth whether salary, bonus, investments, whatever.
And you could perhaps avoid falling into these bands if you were given most of your money to effective charities.