You point out network effects, but that's not the only thing that matters.

An obvious example would be that we do not have one world currency.
Yes, there is US dollar dominance, but people do use different currencies even when transacting on state level.
These are state controlled, so not a good example of the free market.
The explanation here is that various groups (states) want to have control over their money.
The same can exist in cryptocurrency.
Different groups might want to exercise control over their money while the money itself could be identical in nature.
Within the state, people are usually forced to conduct transactions in state currency.

A better example would be the state bank notes that existed roughly from 1790s to 1860s in the US.
These you could exchange for gold and silver coins, but the notes could be used as money.
What killed that was not market forces, but rather gov intervention.

You can think of gold and silver as different forms of money.
Both still exist today.

Cryptocurrency is money + technology, by definition.
So there could be multiple perfectly fine competing money implementations if they offer something new.
And they do exist today.
Lightning is money for people who want faster payments.
Spark is money for people who do not want to deal with Lightning.
Bitcoin is money for people who want trustless payments and that is a good store of value.
Monero is money for people who value confidentiality over the store of value property.
Stablecoins is money for people who do not want volatility and live in the fiat world.

But more broadly even non-cryptocurrency money is technology, it's just a matter of definition.

So in the end, competition on the free market is the answer here.
That could be either a Bitcoin proposal that gets adoption or an alternative currency.