Okay, I can reproduce it on iOS and it is expected behavior.
In the settings turn on open links in in-app browser. Results is expected as promised - in-app web-view.
Otherwise if you set “open links in default browser”, it opens with YouTube app after all because of app-url-scheme, you know.
So, IMHO, all right on iOS.
Is it really needed to create special handlers for special hosts? Where YouTube is there and Twitter and other services. So, how much special handlers there will be?))