@SGaist no, I did not. I just tried it with --qmldir specified and it worked flawlessly. Lesson learnt. However, I feel the deployment article could be a little more informative.
I appreciate the help!
QtWebKit for Android and iOS ? Highly unlikely, since both platform forbids the use of non-native web views and there was no ports.
Taking a quick look at the QtWebView module, there's a QtWebEngine backed WebView when that module is available. So currently you should be able to use that module on all the platforms you are interested in provided that you use a compiler that is supported by QtWebEngine. Note that the compiler constraint doesn't come from Qt but from the Chromium project.