Earlier quoted context omitted.
If inflation is 5% and you get a 5% raise, you're level in real terms, right? No, because that 5% is taxed at your higher tax rate, which is (usually) higher than your average tax rate. This is called bracket creep.
Only if 5% causes you to change tax brackets. 5% of $300k is a lot more than 5% of $100k or $50k/yr, but only if you were already at the very edge of a tax bracket will 5% cause you to change bracket. Eg the 22% bracket is from $40-$86k for single filers in 2021. Only if you were making $81k or more will 5% tip you over. For everyone else earning 40-81k, that 5% doesn't cause a bracket change.
To simplify 100k split 50k @20%, 50k @ 40% is less than (105k split 50k @20%, 55k @40%) / 1.05
The fist is worth 50 * 0.8 + 50 * 0.6 = 70k, the second is worth (50 * 0.8 + 55 * 0.6)/ 1.05 = 69.52k.