I think you are missing the point. If you transfer from an app to a web page, most people will assume they are in their browser of choice. If an app implements its own browser you are not, and have no idea what security you may or may not have, and may continue to use the browser for other stuff. It is a genuine concern for any platform.

I assume the apps track how long you're in the browser, what URLs you open (does the in-app webview forward the URL requests through the app?), I don't know if it can detect how far along you're scrolling in the webview, if it can, then it knows what parts of the webpage has your attention...

It's no wonder most social media apps use in-app browsers.

Oh okay I haven’t even thought about that, because I can easily recognize that I’m not inside my browser but in the app-browser.

But obviously not all the people can make this distinction. As not all the “normal” people are on Hacker News obviously :)