What’s wrong with a “normal” app? No server required and data stays only on the device. The argument that the author is building a PWA because other people abuse privacy (with apps) doesn’t make much sense. Why not build the app, respect privacy, and be done with it?

LocalStorage is not a substitute for an actual database, it’s a cache. The problem with the author’s technique is that privacy minded users clear their browsers from time to time, so they would be inadvertently clearing data they actually wanted to keep because who uses LocalStorage as a persistent data store? Sure it could be used like that as an “off label” use, but generally it’s used to cache what is persistently stored elsewhere or used as a means to avoid multiple network calls in the process of doing something (such as saving calculations, the results of which would be eventually persisted.) Local Storage should be used as if it were a session store rather than something persistent.