I’ve done 1/2 dozen flights with carbon bikes in the cardboard box they came in. Some front wheel off, some boxes are for both wheels off. Haven’t gotten a scratch yet but maybe just lucky. I think that, in general, they don’t pile a ton of luggage on top of bike boxes. Once in awhile though I’m sure stuff gets busted. A guy on my last trip had an evoc bag and it was pretty sweet next to my battered cardboard box.
Joe