> but also using the U.S. tax system to great advantage, putting a very large portion of my gross pay into tax-advantaged accounts[0]
Yep, I'm not an accountant but a 401k for 2021 says you can contribute up to $19,500. But a SEP account for 2021 maxes out at $58,000.
A SEP account is something a contractor or any self employed person can contribute to. It's a tax deferred account meaning the amount you put in is taken off your income right now but then you pay taxes on it later when you withdraw it. Like a 401k, the catch is you need to wait until 59.5 years old to touch it. You can also invest it.
Being able to defer an extra ~40k of income every year is a lot. You could take that 40k and invest it. At 0% interest over 15 years that's $640,000, 3% interest yields $828,593 and 5% interest is $989,456. If you took out your 40k / year at 60 years old, you'd be paying almost no tax on it since your income will be $0 since you're retired and your 828k (middle ground of 3%) would last you another 20 years.
Then there's 15 years of not being taxed on 40k of income at a 35%+ bracket which is roughly 14k a year or another 210k (not counting state taxes which are quite high in places like California and NY). Even if you had to pay $10k a year out of pocket for your own health insurance for 15 years you're coming out way ahead.