Which substandard experience are you talking about? Users never been able to hide the browser UI before, unless the user added the website as a shortcut on the springboard.
So you want to fill the user's limited screen real estate with your own useless crap (usually "download our app and subscribe to our emails!"), and you're worried that the actual functional bits of the browser are getting in the way of your doing that?
There are plenty of uses for fixed navigation that aren't spammy attempts to force app downloads. Users like them. Not all users, but most.