You can only see the haircut problem, not the main one.

I didn't even mention the haircut!

It's definitely not about hedging risk, it's about structurally higher inflation over the long term

But, again, you can hedge this risk, so why are you concerned about it? If the price goes down, you get to buy more HIVE. You then own more units of a less (individually) valuable token with more total units in circulation, effectively the same thing. This works over the short term and the long term. Every time the price goes down, buy some more and offset dilution. When the price goes up, sell a little and offset the deflation.

HBD doesn't provide any long term benefit to hive other than its use-case as a stablecoin

Well, I sort of agree here. The use case as a stablecoin is what creates demand for it, and without demand it would just all get converted to HIVE more or less instantly and not exist at all.