The main problem I see with soft luggage is from other passengers using the overhead bin.

I'm currently traveling (7 legs with one more home) and have witnessed sadly some passengers on each leg perform the following ritual:

1. The passengers on-time have placed carry-on in the overhead bins.
2. The tardy passenger(s) boards huffing and puffing, fully loaded. They then try and push and stuff a combination of attaché cases, purses, jackets, overstuffed laptop messenger bags, etc. on top of the other passenger luggage.

In many cases those bins were filled to capacity, but no matter, Mr. or Mrs. Huff and Puff continue hammering their belonging on in.

3. After looking at their handiwork, just for good measure a few extra hits, followed by either leaving the bin open and walking away, or one more hit before closing the bin.

4. Said passengers then go find their assigned seating, which in some cases is in the back.

Business Class was previously without such conduct, but that too has apparently changed.

Till and others would agree that this practice is all to commonplace in air travel today.

So please keep this in mind regarding soft versus hard shell protection. Your concern regarding theft and handling might include other passengers manners ( or lack thereof ) as well.