Bitcoin isn't controlled by any government yet so I don't see how it has failed it's purpose yet, in the means of alternative, I think that it's a gradual process and it's also next to impossible given that it's going to cause a massive power vacuum when fiat is suddenly replaced by bitcoin, and the financial institutions threatened by it's existence is also trying to hinder the progress because they will get obsolete real fast.
From the pointers OP stated, I believe both items have been successfully accomplished by bitcoin already. It is now an alternative payment method to fiat and it is still free from government control. No government has the sole control over bitcoin as it can exist even without government's mandate. There may be regulation in some countries, but they won't get the sole power over bitcoin's market, because they can't as it is decentralized. So I don't know what the OP wants for bitcoin. I won't consider this as a failure because we will not be here if it has failed its purpose.
With regards to bitcoin being an alternative for fiat, i can see that there is an ongoing process leading to that. But we can't expect that bitcoin could become an instant alternative to fiat without legalizing bitcoin first in countries that have not yet undertake on proposing bills for bitcoin. After legalization, if the government finds bitcoin has more potentials to become a currency, then that's the time they will pass another bill for that. I guess bitcoin to become an alternative currency will still pass a lot of government critics, but as bitcoin has become mainstream these days, the countries will find it more advantage adopting it as a currency, hopefully. So it has not failed its purpose yet, because its still working on its process.
The major obstacle preventing Bitcoin from fulfilling its purpose as an alternative to fiat is its legalization by the government. We know that
the majority of countries in the world still reject Bitcoin as a means of payment, and only legalize Bitcoin as a digital asset. This of course
makes Bitcoin users still rarely dare to use Bitcoin as payment, for fear of breaking the law. But with the passage of time, emerging countries
like El Salvador are boldly legalizing Bitcoin as a legal tender. This is actually a positive sign that Bitcoin is still in the process of fulfilling its goals.
So I agree that it is not to say that Bitcoin has failed to fulfill its original purpose, but rather that it is still in the process of getting there,
maybe the process is not easy and takes a long time. But I am optimistic that in the future there will be a time when all countries will legalize
Bitcoin as payment. So there is really nothing we can do but be patient waiting for it to become a reality.