DeLorean DMC-12 and Renault 25 share the same engine. By your analogy these would basically be the same cars. Which of course is apsurd.
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).