tell me what happens to HBD if Hive crashes pretty badly and in dire straits so much so that HBD depegs?

Systemic risk is not a variable in this discussion.
Again, every asset has systemic risk it's not relevant to the conversation.

There are much better financial vehicles than HBD, with close to similar risk profiles.

Unserious statement lacking a single example.
I have to assume the example doesn't exist because it would be easy to pick apart.

What if I was depending on getting 20% but witnesses decrease the APR to 15% at a moment's notice?

Then you haven't lost anything and can act accordingly.
Trying to compare this to losing money in the stock market is inappropriate.

Tell me how in a scenario where I decided to put 100K USD into HDB, and witnesses deciding to "rug pull" the APR, HBD is more stable and predictable?

Again, you didn't lose anything in this scenario.
I shouldn't have to explain it you should just know.
In fact I think you do know you're just trolling me.
Which is fair play but whatever.
You've gone off the rails at this point.