fire a burst of energy to turn air into plasma, causing a shock wave.
Except the aren't creating a shock wave to counter the incoming wave. They're changing the density, pressure or composition of the medium (air or water) the shock wave is going to pass through, attenuating it.
Have a read of the summary in the patent.
Countering a shock wave with a generated one would be horribly complex. You'd need to measure the wave first or risk amplifying it further. You'd need to generate it at in the exact same time and place you want to counter it, or your own shock wave is going to hit you with the same force as the one you're trying to stop. A tiny error in timing will see twice the damage inflicted on yourself - like the current humidity, air temperature and pressure - all things that contribute to the velocity of the shock wave.