My business had me flying world wide every 2-3 weeks for 3.5 years. The ONLY baggage problem I ever encountered was on a UAL flight from Miami to Bolivia.
I had one hard piece with a piano hinge all the way across the back, and tongue-in-groove sides and front and a hinged lock. The piece was used to carry heavy yet fragile equipment. Before I bought the piece I tossed it around, stood and jumped on it. I'm 200 pounds. I never made a dent in it.

When I recovered it in Bolivia the hinge was pushed in about 1/2 inch. I took it as rough handling, repaired it, and went about my business.

My return flight terminated at ONT via MIA and LAX. I had to pick up my luggage at Miami to go thru customs. Nothing wrong with it then. Recheck it for the flight from MIA to LAX. I saw it being delivered to the puddle jumper at LAX for the leg to ONT, and it seemed to be in good condition, even though the female baggage handler at LAX picked it up and gave it a healthy fling in the general direction of the other bags being loaded. It landed on a soft side suit case, and definitely made a dent in that bag.

When I recovered my belongings at ONT this solid piece, the one I'd bounced my 200 pounds on, had one side pried open more than one inch. The tongue and groove clearly showed scrape marks where it had been pried open. I carried it to the agent and reported the obvious attempt to get at the contents, and she gave me a form and said, and this is a quote I remember as if it were yesterday! She said, "Fill out this form and mail it to the address on the bottom. We'll investigate and see how many times you pulled this before."

I called corporate, told our travel agent I would no longer fly United Air Lines and she should give me a few minutes to confer with my supervisor, the she could call him and verify. I then called my super, explained the situation, and told him if the only way for me to get to an assignment was on United Airlines I'd refuse the assignment. The equipment I carried was owned by the company and they'd have to repair or replace it, but while that was being done I'd be stuck somewhere twiddling my thumbs, and there was a 50/50 chance that it would be a place with bad water, bad food, foul weather, and people not friendly to the US.

I've been retired for about 7 years now, I still enjoy a lot of travel, both in the US and out, and I still will not fly United.