Remember that impact strength and tensile strength are two different things. Nylon filament making up the fabric in a soft sided bag can "give". And thAt is what gives it strength. Hard sided simply don't "give" as much as fabric. Another example is titanium vs tungsten carbide. Titanium has a lot of give which mAke it useful for a golf driver as it gives and bounces back. Tungsten is hard and strong but has no give. It will supply crack.
Stick with fabric. More give. Better longevity.