You again come up with mutually exclusive starting conditions

There is no good medium of exchange on par with fiat currency that would be at the same time as good a long-term store of value. Basically, you have just invented a perfect money, instantiated it (which you can't), and then pitted it against a real fiat currency that is always inflationary and thus can't be a good long-term store of value. Indeed, the fiat currency would lose and collapse, but this approach is meaningless as one can always imagine something perfect, not possible in real life, and ignore this fact