Yup, that's true, it does deviate, but on the plus side, it has some great aerial shots of aircraft, and I thought the crash landing in that movie looked pretty convincing. And there are recorded instances of people doing that sort of thing.
In fact, there is an instance of that in one of the books I recommended up on the post above, where in Johnnie Johnson's book, Wing Leader, he relates the story of one of the squadron pilots bailing out over the English Channel in just such a fashion. The pilot in question could see that his flight leader was in the water, wounded, and consequently could not get into his liferaft, so he too bailed out in order to help him. Sadly, in that case, both pilots were never heard from again.
So stuff like that really did happen, and you can understand them putting it into movie adaptations of books to make them more dramatic, even if it is a bit 'Hollywood'.
Chock