Just because we made something up doesn't mean there aren't different levels of stability for that made up model, or different levels of real world results from acting on those models.
What it means is that there is no “real” justification for something to be valuable, is what people agree on. If enough people agree that crypto is valuable and want to buy it, then it is valuable for as long as people believe it is. Just like any other form of currency.
Just because we made something up doesn't mean there aren't different levels of stability for that made up model, or different levels of real world results from acting on those models.