I wonder how much of the damaged instrument belief is myth? There are people that will do anything to carry on all the luggage they can because they believe that the chances of their stuff being lost is so high. My experience in these matters is that luggage is almost never sent to a location other than it is supposed to go to and that rare time when it is wrongly routed it has been located and returned with apologies within 24 hours. My experience with insturments is not extensive but other luggage properly packed seems to arrive in tact. Are there exceptions? Sure but I bet more instruments are damaged due to poor handling in private vehicles, taxis and by 'friends' than in airplanes. I have seen inconvenience but not damage. (Your milage may vary.)
I suggest there is more paranoia and myth here than fact.