This is the article by the baggage handler noting that hard cases can slip off the conveyor belt especially if it is wet outside.
https://cyclingtips.com/...m-a-baggage-handler/ Interestingly, somewhere in the ST forum you will find a guy who was travelling with a hard case that slipped off the luggage cart and then was run over by a fuel truck. It crushed his case and his bike. Oh well, sometimes it just doesn't matter what you do.
I've been travelling domestically and internationally with soft sides for about 12 years now and no damage (PikaPackWorks and now a Thule Roundtrip Pro XT). But if you pack your bag correctly, it should be able to handle many bags piled on top; a significant drop, side impacts, etc. That requires breaking the bike down, using fork locks, removing the RD, padding all frame tubes, using semi-rigid side inserts, and eliminating loose items inside that could damage the frame. Besides lower weight and size, one key advantage of a soft side over a hard case is the ability to flex when TSA opens to inspect, and then re-closes the case. A lot of reported damage you read about is when TSA forces a hard case closed when parts have shifted. In the end, there is no perfect case and we are all just trying to do our best to get to the destination.