> Take Arweave, for example. There you get indefinite storage for a one-time fixed fee. This is based on the extremely conservative assumption that storage prices will decrease by 0.5% pa on average. Over the last 50 years, it was something like 30% pa.

It's based on a lot more than that. The fact that you can go through their entire webpage without them even trying to explain the risks to their potential users is downright shady.