“Asset Browser” is kind of a vague concept. There’s actually two kinds of asset browsers. The project asset browser, and the artist asset browser.
For managing the assets for a particular project, like, say an animated film, or a game, you want your assets linked in, and indeed changing one should result in all of them being altered in all the files in the project.
However, this would actually be actively bad behavior when you’re not dealing with assets that are common to a project. When you’re making something one-off, or at least are using assets that you expect will be baked into larger assets, what you want to do is directly copy them into your files so that you don’t have any dependencies on your particular library. Imagine you made a car, and you linked in some wheels that you have in your library because you make cars often. Your car would then be dependent on the wheels being in your library and you definitely don’t want that when you ship that off to wherever you’re supposed to ship your work off to.
From the scant documentation, it seems to me that the asset browser is currently intended to solve the latter use case rather than the former. I imagine tackling project asset management will come later.