I've seen some luggage tosses that missed their target also. Speed is important, but not at the expense of reasonable care. If you have the gate number and time of the incident, a letter to Southwest might help them correct the problem. After a given individual accrues several letters, that person at least will no longer be tossing bags with wild abandon.

Is this problem worse at Southwest than at other airlines? That's plausible, for the reason you state: short turn times. But I don't think we have any way to know, other than by looking at baggage claim statistics, and those don't show this.