I haven't mathed this out, but from experience from jumping (both from heights and towards ledges) I would think that our arms and legs are much better shock ab

I haven't mathed this out, but from experience from jumping (both from heights and towards ledges) I would think that our arms and legs are much better shock absorbers than our ribs. If you hold something like a shield, you are primarily using your triceps and shoulder muscles as springs to dissipate the impact over the distance of about a foot. Of course there are issues with that, but it's much better than your rips which can move much less before breaking.