Here's a super slow motion video I did of a set of longbow limbs I mounted on my old compound riser. They make a 68" bow. The limb preload is pretty light which I believe is why the limbs flex so much. I did the same with a set of recurve limbs mounted on this riser and they flexed quite a bit too but not as much as these longbow limbs.
This video is better if you use full screen