Python would like a word with you about point 1)
I love Python but people over state its benefits and effectiveness.
So at the moment, I am using PyQt/PySide and load my HTML/JavaScript/ReactJS GUI in a webview with a simple bridge object between my Python code and the JavaScript code.
As soon as I need native interactions with the file system, etc., I am using Python, which is robust and proven (and I am used to it). For example, if I need a dialog to save a file, I just use QFileDialog.
At the end, because of a clear separation between the GUI and the computation/system interactions with the bridge object, I just need a different bridge object to have everything running fully online.
One point is of course that I am not developing for phones and tablets, I package everything with pyinstaller for the good old desktop users.
The main hurdle that other languages faced was not having a native UI. For example, GTK on OSX or Windows did not feel native. Key bindings were often not native. Similar story with Java (was it Swing?).
The HTML/JS/CSS combo has exactly the same issue (it's not comparable to a native GUI - Cocoa or whatever it is.
Electron faces this same hurdle, but with a twist. It just doesn't care; it picks a rendering target (the web) and simply uses it everywhere. Perhaps that's the approach QT and others need to take as well: stop trying to match Apple's UI on Apple, and Windows' UI on Windows.
Great idea, but make sure it at least looks/feels good.
I remember Swing stuff from the late 90s and... IMO the primary issue wasn't so much that "it doesn't look like Windows" but that ... it was a very poor experience.
Copy/paste/keys - yeah, that's an annoyance, but if the UI is clean, friendly, easy to understand and be productive on, people can look past the differences of the native host OS. Swing (and GTK and others) really don't provide a 'better' UX (imo).
C# might even cover that now.