I think you have it right: Bitcoin is a way to move fiat. But it's the network, not the coin, that has the value. All of the transactions being done in BTC could be done if BTC were worth $500 or so. Everything else is basically a form of seigniorage.

Bitcoin can't be counted on to hold its value because ti must only hold its value long enough to be bought, sent, and sold. Its use case does not depend on its long-term value, so nothing but bigger fools supports that value.