Arguably many users don't know how to use a Windows desktop. But that's not a failure of desktop; that's failure of Windows. They could have provided an easy way to install applications to a sandbox. On Android you can install from apk files and they are installed to a sandbox. If Windows had such a feature easily available, I think most of genuine desktop app makers would have migrated to it. This would have the advantages of the browser and no battery drain, no fan noise, no sluggishness.
It is not that OS developers are not improving , for example S mode on surface is a good feature, however as long as adobe’s of the world still abuse my system the problem is not solved .
It is just not older gen software either , Slack desktop definitely takes more resources than web version while delivering broadly the same features Sure it is electron abstraction , however if a multi billion company with vc funding can not see value in investing on 3 different stacks for windows,MacOS and Linux how can most other developers?
Unless your domain requires high performance(with wasm and WebGL this will also be reduced) or something niche a browser cannot not currently provide it no longer make sense to develop desktop applications. The native application is too much hassle and security risk for the end user compared to a browser app and is worth the trade-off in performance for vast majority of usescases.
While the browser security sandboxes have its issues, I don't want go back to the days of an native applications constantly screwing my registry, launch processes , add unrelated malware and billion toolbars to your browser ( java installers anyone ?) .
Till late 2000's Every few months I would expect to do reinstall the entire OS (esp Windows and occasionally OS X) because of this kind of shareware / malware nonsense native apps used to pull. While tech savy users avoid most of this pitfalls maintaining the extended family's systems was constant pain. Today setting a chromebook or surface( Default S mode enabled) and installing an ad blocker is all i need to do , those systems are clean for years.
I do not think giving effectively root access and hoping that that installing application will not abuse is not a better model than a browser app. It is not just small players who pull this kind abuse either, Adobe CC suite runs like 5 launch processes and messes up the registry even today. The browser performance hit is more than worth not having to deal with that
Also just on performance from a different point of view, desktop apps made my actually system slower, you would notice this on fresh install of the OS, your system will be super fast , then over few weeks it will slow down, From antivirus to every application you added , they all hogging more of my system resources than browser apps do today.