As far as I know that's not accurate and the default webview on Windows is still the old Edge based one, not Chromium.
The plans here are somewhat unknown I think, but right now you have to force the user to download and install (or bundle an installer) for WebView2 or Edge beta channel if you don't want to support old Edge.
Gtk-webkit is also quite different from Safari, you can't assume they are just the same.