You would have thought so but it doesnt. I have seen demonstrations and numerous videos at QinetiQs acceleration/deceleration track over the years. They still had some of the Kegworth seats there years after the event. Whilst we can all sit here pontificating and theorising on what may or may not work, we forget that there are real experts out there using very expensive equipment who spend their lives looking at and researching into these things for our benefit. Believe me when I say that they have probably tried every combination of posture and restraint, using post-mortem studies, to produce the recommended brace position that we see today.
I saw films of crash test dummies which had their legs forward as you describe. It is not a pretty sight, even on dummies, as there is still enough forward momentum on the lower limbs to fracture them on the rigid seat frame in front.