If he wasn't messing around, he wouldn't have missed those hits. Finn wounded him, and even more than once...
Why couldn't Ren just take his lightsaber with the Force? Or push him away with the Force, like he did with Rey a few seconds earlier? Based on what I've seen before, he could have taken down a stormtrooper in dozens of ways in a couple of seconds, but in reality, he couldn't do anything to him for ten minutes.
Where do we end up when we save the world?