Windows OS has a dominant market share yes, but do those people download and install a lot of desktop applications? Especially on a platform like Windows, where a browser can do almost anything a native app can do?
The counter-argument is that it is that everyone has a web site and if you want to make something that is really different and better you need to do something different.
For instance I use em client as a mail program and fastmail for the back end. It's a lot like MS Outlook except that it actually works. I prefer it to GMail.
With the rush to Electron we see developers leaving so much performance on the table, particularly with the rapidly increasing core counts.
There's also an argument that the "web" is no longer an open platform but is now becoming the "Google Platform". For instance you cannot trust conventional web sites from a privacy viewpoint now that most of them have numerous third-party trackers, download content from multiple CDNs, etc. This deviance is not so normalized for desktop apps.
