React Native's new architecture is not that bad.

You basically just got a single lightweight JavaScript thread that runs your update loop around which components should be rendered and updated, but then all the components are bound directly to underlying C++ native components.

I would still expect the start menu to be aiming for zero dependencies and as fast a start as humanly possible, but it's not that crazy compared to something like Electron (which itself is not as inherently bad as most people make it out to be).

The real problem with slow web apps has less to do with the architecture of the apps, and more to do with them letting developers build apps really quickly and easily, meaning that you often have apps built by developers who don't entirely know what they're doing, and they introduce tons of inefficiencies like double rendering etc.