1. This could be checked. Have other assets with similarly huge runups followed a power curve this closely for this long?
2. If some rapidly appreciating assets do tend to follow this curve, then that's a reason to expect bitcoin to follow this particular curve, too, rather than the infinite set of other possible curves.
3. If damn near every asset follows this curve (with different parameters, obvs), then it's the fit parameters that are the interesting parts.

Conditional on bitcoin not dying, it's kind of a high probability that it'll trade within their stupidly large range

This isn't right. If bitcoin stabilized at $60k, it would be highly divergent from their bands very quickly.

Now, if you're saying that it can't do that without dying, then I think you're sort of making their point.