Random swings in Chambara (swordplay) will actually make your attack weaker! But you can try to slow down and land one blow at a time by gently swinging your Joy-Con controller.
With the Charge Sword, you can press the guard button just before an opponent’s attack to try and get a “Timely Block” that will send your opponent flying backwards a great distance. You won’t be able to pull this off if you mash the button!