You may be right, but it's also not as simple as you make it sound. There are a number of discontinuities in the bottom line rates that can make a much larger difference than an increase in one's highest marginal bracket. Especially around the income that the Henderson refers to, when you're likely to be hitting the AMT, it's definitely not a smooth function.

For myself, a year and a half ago, this happened. There was a conjunction of several changes (particularly hitting AMT, and a significant decline in mortgage interest deduction, and a good chunk of additional one-time "unearned" income) that together made it appear that the marginal rate on the income (relative to the previous year) was on the order of 60+%.

FWIW, I know that it's a (hideously) complex calculation with many, many factors, and what I was looking at thus wasn't actually the marginal rate as such. Nevertheless, what I experienced was, financially, the equivalent of that.

Your point portrays this as simple by assuming that the income tax is represented by a simple set of tables, but it's much more byzantine than that. All this added complexity can sometimes make your best-case scenario turn much worse.