You certainly don't see competitive sporting clay, skeet, and trap shooters with anything that short. But, I'm sure it's fine for a stationary target.
The card shooters also use longer barrels. Although the forcing cone, amount of backbore, taper and amount of choke are very important, length is also a contributing factor. As far as card shooting goes you cannot make a 21 inch shoot with a 32 inch. May not be a big difference, but when money is on the line you take every advantage.