Just to be clear: I'm not saying that the theory that Vader or Sidious drained her life force to keep Vader alive is either obvious nor the only possibility. It could just be bad writing. For me it's just a theory that happens to be supported by some of the imagery and editing choices in the scene and it has just the right feeling of myth making about it.
You'll get no argument from me on that last point.
That said, Lucas has a very particular way of telling stories that's taken me several decades to really get a handle on. He's a visual storyteller. The process of writing doesn't come easily to him and he knows he's not very good at it. He's most at home behind the lense and in the editing bay.
With that in mind I've found if one wants to really see what he wants to say, it's often more illuminating to ignore the words and the performances and just focus on the images. The composition of the shots, the pacing and editing beats. There's a lot more between the lines in these films than most people give them credit.
It also helps to remember that the intended genre isn't science fiction, it's a fairy tale. A fantasy myth that happens to take place in space.
So when you look back at the dual birthing scene, try doing so with an eye towards the mythic. Note how she cries out every time he feels pain. How she gives of herself as he is locked away within himself. How as he takes his first breath, she takes her last. How her last words were of him and his first were of her. None of these things are a coincidence, or just done for shallow poignancy. This where you'll hear the voice of the director because that's his volcabulary.
