The default YouTube app in iOS was great back in 2007, but it hasn't seen a significant update in years and is lacking many features compared to the newer mobile YouTube website that Google launched two years ago.
To stop iOS from launching the native YouTube app, and force it to use the superior YouTube mobile website, simply disable YouTube under Settings > General > Restrictions.
This will make all YouTube links open the mobile website and will also hide the native YouTube app on the device. If you decide you want to revert these changes, simply go to the Restrictions settings and toggle YouTube back on.
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