I could be wrong but I feel like literally running some kind of little mini virtualized instance and just running a desktop app meant for OSX or Windows could end up being more efficient than running a whole browser.....
Not necessarily. If you're running the browser anyway, and the app is a PWA and can share that same instance. The "browser" overhead is not really there.
A native app, lets say that wants to play video and is using a cross platform GUI. You've got to load and run that code, and have all the relevant code in the native app's address space. That would be a bunch of code that needs to load over the PWA which is leveraging something you have loaded in RAM anyway. In this case the native is actually worse than the PWA for resource utilization.
Launch CPU cycles can be similar, running a huge swath of GUI code for the native app vs a pre-loaded browser which only needs to run the JS and render the page.
Having your app's runtime already loaded on the system is a huge advantage.
Electron does not benefit from these advantages though. These are PWA exclusive advantages.
