I agree with your assessments in general and thank you for additional information.
I disagree with a conclusion that HBD interest payments are only there to benefit 1%. It is open for anybody who is willing to use this feature and earn stable income on their money. There is a risk of missing out for those who choose to use HBD savings though. These accounts will miss out on big Hive price movements. The system is fair and everybody is welcome to participate in interest payments. That's why who is getting how much becomes irrelevant.
Also 20% APR is there to attract investments into Hive. Because the supply of HBD is so low, the only way for anybody to acquire massive amounts of is by minting - buying Hive and converting them to HBD. This in return should increase the price of Hive. If this theory works in practice, it is a win for the blockchain, for the community, for Hive/HP holders, and HBD holders.
So far, we don't see massive adoption of HBD, mainly the same people are using the savings feature. In this regard 20% APR wasn't able to accomplish its goal yet. But this also means, Hive doesn't pay too much out in interests, and these numbers are so low, there is nothing to worry about as far as sustainability.
As far as Hive price, I would rather see it keep going up slowly and consistently. Sudden and short lived price jumps don't really mean much.