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Is 40% sustainable though? HBD is a long term solution. That's why witnesses try to stay conservative to make sure this is sustainable in a long run and doesn't cause any issues for the blockchain.

20% seems to be native and the rest is the Thor platforms doing, but it's paid in UST.

Is it sustainable? Probably the market has to decide, it might very well be. If you can transition only through the 'native main' token, it absolutely is nutz and will crash... But, adding to the mix some direct listings of the stable coin to DEXs and CEXs, there's just no reason to grow slower than what the market is willing to swallow. Lots of those will be devoured by Swaps and Pools anyway, quasi SIPed out of circulation while boosting the main tokens ecosystem. Inflation speed is absolutely reduced to being only a number, as long as the liquidity is not crashing the internal markets.

Or am I missing something important?

The demand for algorithmic stablecoins might be in the trillions, well, very probably is in multiple trillions over the next couple of years. That's literally a tremendously huge cake, maybe grab a piece or two.