You're imagining the tax rates as being much higher than they would actually have to be (and I think you also missed that the taxes you pay always end up being a tax-rate proportion applied to the amount you earned that year). Assume for simplicity that people typically have a 40-year working life.
Then when you earn your first $500k in five years, that will be taxed at a rate appropriate to someone who earns $500k over their working life (that is, $12.5k/year). What's the U.S. tax rate at that level, currently? 15%?
So I envision your annual taxes, in your example, as looking something like:
Year 1 Earn $100k Rate 10% Tax $10k
Year 2 Earn $100k Rate 10% Tax $10k
Year 3 Earn $100k Rate 10% Tax $10k
Year 4 Earn $100k Rate 15% Tax $15k
Year 5 Earn $100k Rate 15% Tax $15k
Year 6 Earn $10k Rate 15% Tax $1.5k
Year 7 Earn $10k Rate 15% Tax $1.5k
Year 8 Earn $10k Rate 15% Tax $1.5k
Year 9 Earn $10k Rate 15% Tax $1.5k
Year 10 Earn $10k Rate 15% Tax $1.5k
You won't move into the 25% band until you've earned something like $1.3m over your life.
Then when you earn your first $500k in five years, that will be taxed at a rate appropriate to someone who earns $500k over their working life (that is, $12.5k/year). What's the U.S. tax rate at that level, currently? 15%?
So I envision your annual taxes, in your example, as looking something like:
You won't move into the 25% band until you've earned something like $1.3m over your life.