chain stay protection on carbon frames
My experience is that they help minimise the damage.


By being malleable and typically having a foamy backing (for shock). Usually only good for a few impacts. 
By having ~1mm foam and being somewhat rigid it may help with less aggressive sucks. 
But if they were stiff and had no tolerance toward the frame, it would mean all the force would transfer through and damage the frame at the edge of the protector. 


Chain suck typically has a range of causes and is very noticeable and should be addressed straight away.

I wouldn't see it as a weak design part, more in line with something like a crumple zone of a car that is meant to give way, if that makes sense.