@Recherei: I must admit that the working "hypothesis" makes sense, but unfortunately it is just that. We can not be sure how the luggage is handeld, and even if lighter bags are really given extra care by airport personel, it can still end up being shifted around or turned upside down or thrown down during the transfer progress.
Especially over the last three years, I flew quite a lot across Europe (@ once a month). I can say that I would never ever take the risk in using cardboard boxes for something as valuable as a suit head! After every journey, my bag was a bit more destroyed than before.
My last suit case (medium quality) lived for one year and 2 months until I could not use it any more.
The suit case I use at the moment (good quality, it is 4 months old) already has deep scratches and a torn off zipper.
I am not going to advertise flight companies now, but I am using 5 different companies operating in Europe, cheap ones and "better" ones, the impact on he bags always beeing the same.
So especially for suit - heads I advice cases with hard plastic shells, alluminium boxes or: if small enough, take them in the plane as hand luggage.