A soft case is still too big and bulky to ride out of the airport with it. You could roll it and put it in a locker at the airport though, but I don't think any airport still has those post-9/11.
The big + of the soft case over the hard one is that it can be rolled and it can be bullied into fitting into XYZ space (even with the bike in) while the hard case just can't. With my partner we had a very hard time finding a cab that could fit the two of us, our bikes and our suitcases arriving in Montreal. Even in a minivan it can be tricky. I could fit everything in our 2 door hatchback Honda Civic but it meant about 30 minutes of struggle and using every cubic square centimeter of space. Hard cases would not have fitted the Civic!!! When renting a car abroad, we could do with a very small vehicle.
The US and Canada have quite modern airports, and so do most European cities, but once out of the airport, not all buildings and public transport stations have elevators, wide doors, etc. Many, many European hotels do not have elevators. Etc. For me it's important to be able to carry all of my own luggage on my own, on all sorts of terrain. The soft case is bulky, but less heavy than a hard case, and I can somewhat easily carry it on one shoulder while carrying another suitcase/bag with my other hand. If I was 6' tall it might be a different story, but I'm 5'4".
Following your advice, I'd be a little more wary of travelling with that in the US. However when I've flown in Canada I've found that they were really careful with our bike bags. Once, from the waiting area, we could even see two employees carry them into the plane and they were more careful than I am with it!!! On Air Canada planes at least they have a special container for sports equipment, in which they don't put suitcases and regular bags.
Ideally, I think we would have both types of cases, plus clear plastic bags for those occasions when we'd want to ride directly out of the airport (loaded touring).But considering the price of the cases (our soft cases are well padded and were expensive), that's not an option for now! Maybe in the future....