Yes, some of these stunt type presentations really draw some questionable conclusions. Especially since you can stop the vid and see that he does "shoot the cannon from a canoe" in Braden's words, as he has lifted into the air in the film. Also it is quite obvious as you say, that creating 2G's of force on the ground in no way assures it will make it to the ball. There are a multitude of ways that the power can be lost along the chain up to the racket. Also if you took a high jumper and had him jump as high as he could and serve a tennis ball, the G forces would be greater than recorded here, but his serve would not come close in speed to what Tanner did. Using data in this way would actually support an inverse relation, which is clearly is not what Braden intended. I do think info from the plate could be useful, just not as presented in this vid.