Except they use their own browser features, sync, telemetry, privacy practices, business model etc...
Engine just makes the car move, everything else defines it. Same with browsers on iOS. Also saying Chrome and Safari on iOS are same browsers because they share WebKit is like saying Edge and Vivaldi are same browsers because they share Blink (they share much more, but still they are very different).
It's like using a winforms webbrowser control in .NET and giving the window a title with your own brand name.