Bitcoin is demonetising gold.
Bitcoin transactions are also "irreversible" providing the fee paid is reasonable, but ultimately the clearing time for both networks is down to the likelihood of a 51% attack for which bitcoin is far more protected against due to the far larger amount of hash power. It's not comparable.
If I'm moving/storing $1 billion, do I care if the transaction costs $1 instead of $20? No - I care that I'm storing the money in the safest place to store value I can find.
So even if fees increase in fiat terms, so will the size of the transactions. Enough to take the market cap far, far beyond that of gold. Once bitcoin has grown to the point that its value has stabilised, there will be substantial demand for transacting in it directly and there will naturally be a lot more work invested into higher-level payment networks/solutions. Right now though, Gresham's law sees to it that most people are happier to hoard than spend and that's likely to be case until bitcoin is at least $10M/BTC
> The slowness and simplicity of the Bitcoin network is what gives it robustness, and if I'm storing large amounts of money, that's what I want even if it means I can't buy a cup of coffee on the same network.
Then why not just use gold? It is slow, simple, and you can't use it to buy coffee.