There are some reasons to go with the soft case. The one I am talking about is the BikePro case, as compared to a hard shell case like Tri All 3.
First of all, it can be shoved into the back seats and trunks of cars that you would never get a simialr sized hard case in, ie a normal taxi or rental car. It can be stored in a smaller space also (wrap a couple of luggage straps around it and it rolls up to about half it’s height.
Second, you need to compare the weights. On some airlines, you only get 50 pounds for the bike unless you want to pay the overweight fee. With the hard case going 35 pounds, you better have a pretty light bike. Other airlines give you like 80 pounds, which is much better.
Third, you can carry the BikePro case with a shoulder strap, rather than having to roll it (assuming you are a fairly sturdy person). This becomes a big deal when you hit some stairs. It has really nice wheels and rolls well also.
As far as protection, the idea of a “soft” case seems a little weak, I agree. However, it is not really soft, it is solid metal on the bottom, and has a plastic liner on the side, so it is really only the zipper area that is “soft”. In practice, it comes down to how well you pack, Properly packed, there is no way your frame can get damaged, I think you could run over it with a truck and have it come out without a scratch. Thin carbon wheels I am more concerned about. The wheels sit between the side and the frame, so I can envision a scenario where a lot of weight is placed on the side of the case, and the wheel is supporting that weight with a small contact area against the frame. So far I have had no problems, but I’m thinking about adding some thick heavy foam to the wheel bags to offer more protection for the wheels. I’ve used some PVC across the width of the case to try and keep any side loads off the wheels if possible, so far so good.
Then there is the durability of the case itself. I’ve seen and heard a lot of stories about cracked hard cases, casters and latches getting tore off, etc. Maybe you don’t hear these stories about the bikepro because it is not as common, but maybe it is just more durable. It sure seems well made.
On the down side, you have no place to attach stickers 
Since I have not owned both, I really can’t say which is best. I just wanted to point out some of the factors to consider. I’m happy with the BikePro and it has not let me down yet.