You have a point that for some applications, mainly the "some textboxes and buttons" variety used in things like data entry are better served by a webapp. As for other things every time I scroll up in a html5 chat application and the fans of my laptop go WHIRR I'm reminded that for anything non trivial you are still better off getting your hands dirty and start using a good GUI framework from the language of your choice.
For a while I thought that WASM will bridge this gap and bring a future of near native performance to webapps then results like the ironically named sixtyfps[0] toolkit having trouble pushing 20fps on my 2 year old flagship phone made me skeptical whether it will ever happen.
[0]: https://sixtyfps.io