You have made the same mistake nocoiners make when seeing shitcoiners and assuming bitcoin is part of that.
Almost everyone talking stablecoins is a fucking retard. In fact, it could very well be 100% other than myself, which I take no pride, in fact, I find it shameful to belong to such a species, but I digress.
Anyway, your axiomatic flaw is that you are discussing equilibrium states, which is nonsensical as we are not only not in an equilibrium, but we are approaching the most sudden economic singularity human history will ever witness.
You state ~dollars are not better than bitcoin as a unit of accout, but this is 1) wrong; 2) as nonsensical as people who say "bitcoin cannot be bitten like gold". Your statement "because this is a solved problem" is a logical non-sequitor -- perhaps you meant stablecoins are no better than dollars? When you have a complete understanding of Unit of Account, it all becomes a lot simpler. As the post a year ago asking about a bakery with prices fixed in bitcoin demonstrated, using bitcoin as your price will cause economic trade relationships and businesses to fail (sort of like an impedance mismatch -- you are vertex n + 1, with supplier as vertex n, but there is a web of customers in front, and lower tier supplier behind your supplier that are all on a different standard, which is volatile with respect to yours).
Unit of Account is actually a lossy compression of Measure of Value plus Standard of Value, and when the latter is considered, two things became easy to admit as obvious 1) the US dollar is far and away the best monocomponent Standard of Value in the world today, and 2) the only thing that can beat the dollar on this measure is a multi-component / composite Standard of Value into which a fraction of bitcoin can be introduced. It is at that point where the discussion of a composite stablecoin vs a fictitious/emergent "composite coin of currency" that is realized as the implication of a complex sequence of forward contracts withing relational trade, labor agreements, or short term trade credit, lease agreeements, and so forth.
I truly tire of being this far ahead of fucking everyone for a 2017er, and this after openly sharing all this for two years (not to mention, it's been around since 1875). Kafkaesque af