Sorry, I think it’s just bad communication on my part (or perhaps some confusion with the OP’s question). I think OP’s husband was concerned that the 9% rate is total over 5 years, so thus only about a ~2.2% effective rate. This certainly isn’t the case.
I didn’t mean to present any scenario or example of the rate resetting at exactly 9.6% every 6 months over the next 5 years. If it did, then your math works.
Everyone should keep in mind that no one wants the rate to stay that high (unless you have alot more invested than you spend). The $10k-$15k that I expect to invest in I-bonds annually will only alleviate some of the pain of inflation reducing the purchasing power of my pension and 401k balances during retirement.
ETA: the other benefit to these bonds is that they use CPI as their baseline, and CPI tends to over-state actual inflation. So that can be a big plus.