These are highly inaccurate calculations. We should consider daily emissions of HBD to authors as well to get full picture. There is roughly 50-80k HBD peinted DAILY as rewards to authors, how does that change a picture you paint? HBD is highly accessible for active and dedicated authors and each person wanting to take a risk of staking slightly underpegged asset is free to do so.
As far as the same data brought by @penguinpablo states people choose to CONVERT these superior asset back to HIVE. And powering down en masse is simply not visible.
Your mere APR calculation doesn't include risks/rewards ratio and utilities of tokens and proves nothing in this case.
The HBD received by authors comes from inflation on the HIVE and not the interest on HBD savings. We can see this because the HBD rewards received for a post dips when the price of HIVE dips and rises when HIVE rises.
Coingecko shows that the HIVE price has been falling faster than the BTC price. If the high interest on HBD savings worked as planned, the price of HIVE would be rising right now.
If the high interest on HBD causes the value of HIVE to drop (which is the most likely case); then the HBD interest hurt HIVE authors.
The transfer of funds from HE to HBD is visible. You can see this if you followed HoneySwap or simply look at the coins on HE which have fallen steadily after the HBD announcement. Again, I can show you dozens of accounts which dumped their free HE tokens and then transferred funds to HBD.
The impact on HIVE probably won't happen for a year. HBD interest is relatively small. The interest compounds and we should start seeing much larger payments per month.
Trends you discribe are nothing outstanding in given conditions. While market tanks, smaller coins tank even harder. During last bear barket BTC lost roughly 80% of its price, at this time most of altcoins dropped by 95% and more. This is asimple risk management by investors.
Obviously HBD rewards come from inflation, but you missed the point, HBD interest is a drop in the ocean while compared to author rewards, hence irrelevant and your theory doesn't stand in the light of these facts.
HE tokens are extremely nieché and risky investment for a long term. It's no surprise these might tank even harder.