So I’m supposed to maintain a native app for each platform and try to be sure they’re aligned in every way except visuals? Sounds like a recipe for bad UX if anybody uses more than one of them.
Memory use alone is an interesting case for comparison because websites tend to have a lot more images/videos loaded than other applications. All of those PNGs and JPEGs need to be decompressed before you can paint them to the screen which makes them much larger.
A web browser is a huge platform. Audio, 2D and 3D graphics, file handling, network requests,... A lot of code while your application needs are tiny. That is wasteful and a security risk.
If you go Rust all the way all you need is the installer for each platform
The core contains the logic all the underlying platform uses and the platforms only handle wiring and ux