I'm not sure I agree, at least not exactly. I see your point but my response would be that Bitcoin could be a currency with a very special use case, and in this space be a functional "currency" but this word is being stretched in a sense.
Here's what I mean, Gold can be used to buy things but is it a currency? Not in most people's estimation of the definition of currency or money. But yet it can be used to buy somethings, sometimes, with some people.
And gold can be used in enough situations that it has established itself in the minds of an adequate threshold of people as a thing of value.
To me this is the question as to whether a thing has value or not? Do an adequate number of people agree the thing has value, whereby the community that do accept it is sufficient for one to reasonably rely upon that object or thing as a "currency" or money?
In the case of gold it would be hard to buy groceries with it, but you could probably in certain situation with the right connections buy a property with it. Not easily but possibly.
I see bitcoin in the same way, could you easily buy your groceries directly with it? Not today, not with the fees, transaction delays and price volatility. But could you buy a plot of land with it? Not easily but possibly.
So it is a medium of value exchange, but with a very niche function.
Does price volatility hold Bitcoin back from mass adoption as it pertains to being a functional currency, yes. But yet people are using it now through cards like TenX.
In November alone 20 million dollars was spent on the TenX card, across a user base of 100,000+ users, in Europe alone. And right now those purchases, and that card, are entirely funded by Bitcoin.
So some people do use it as currency, and more will next year, despite it's volatility.
Conclusion:
If you are asking if volatility holds back BTC's mass adoption as a currency, I think the answer is yes, if you are arguing that BTC cannot be a "currency" until it stops being volatile I think you are objectively, and verifiably, incorrect.