> An alternative, which doesn't require insane loading times, is to use any of the many great Python libraries that allow you to write web apps in Python

Sure, there are lots of things that do that.

They don't let you build apps using the Python scientific stack that live entirely in the browser, because they tend to be transpilers plus implementations of a subset of the stdlib plus some browser-specific libraries, whereas PyScript bundles WASM-compiled versions of important Python ecosystem libraries.

They have different strengths.