I don’t see the point of being able to change the UI skin only? All that does is tricks people into thinking they’re using a different browser when they aren’t, and it gives Apple control over which features and APIs are supported etc. (maybe you can patch new ones in by injecting a polyfill but that’s a terrible solution)

It limits what plugins/extension can do. For example Firefox on iOS doesn’t support plugins at all and thus you can’t use the same Adblock you would use on desktop (unlock origin)