Why the power law is a model: because it makes an hypothesis that time is the real driver (or something that is a function of time) and the growth of the system scales up as the log of time. It is a powerful hypothesis and given we are dealing with a power law it has scientific validity and meaning. Do you know much about power laws? I think not. Maybe you can read about them online, there is a ton of material. But basically the essence is that power law say something abotu the intrinsic nature of the system. This is why you can use it to make predictions. It says no matter what happens externaly BTC will continue to behave in this way, in fact as it scales up it becomes more robust and stable. As any hypothesis it can be falsifiable but it is a power hypothesis and makes this not just a philosophy as you say but a model that is by the way very useful (I call the bottom with it for example in 2023).