The contoured side panel looks like a good design feature and it is essentially weightless. As I read, I wondered if load lifter straps are actually accomplishing the same thing--- not that they are a better alternative, but they tweak the top of the pack to fit the shoulder curve in the same way. If so, the side panel contour has the advantage of less hardware, assembly cost and lower weight.
In looking at the photo of Will and the pack with gaps, it brought to mind something I have seen with others on the trail: some hikers don't tighten their shoulder straps properly and the pack is an anatomical mess, rotating down and out away from the shoulders. In the photo of Will, the pack has some large wrinkles, indicating to me that it may not be over filled and just worn too loose on the shoulder straps.
The side panel contouring looks like an excellent choice for pack designs that don't continue above the shoulder strap upper connection. In those designs, load lifters are a useless addition I think.
As far as s-curve cuts that contour into the lumbar area, I think that some lumbar curve is quite helpful to distributing the load to the hips and more stable as well as more comfortable. Getting the right torso length is critical. Note that many internal frame packs have curved stays and the option to tweak them to fit the user. Also, with unframed packs, proper loading and use of side compression straps can add a virtual lumbar curve.