"I suppose there might be a situation where you would save more taxes doing the QHFD, ..."
For all practical purposes, never for those over age 59½. For those over age 59½, AGI ends up being the same whether the HSA contribution is done as an HFD from an IRA or is instead done as an ordinary IRA distribution followed by a deductible HSA contribution.
The only case where there would be a taxable difference is if the individual had basis in nondeductible traditional IRA contributions and for some reason wanted to preserve basis to be applied to an IRA distribution in a future year when the marginal tax rate is expected to be higher than now. HFDs come only from the pre-tax portion of the individual's IRAs. (Note that it would make absolutely no sense to make an HFD that exceeds the pre-tax amount in the individual's IRAs since the result of doing so would effectively subject the after-tax portion to taxation a second time.)
