Overhand Accuracy

How often have you heard that overarm strikes are inaccurate?  I can't do this with an underarm strike, and I can do this repeatedly for minutes on end with overhand.  A tennis ball is not all that much bigger that the eye hole of a helmet.  This would ruin your day.

If anyone can do this in underhand, please post it.  This is a 9' dory, held back beyond the point of balance so that it was quite front heavy because I took the sauroter off the shaft for storage- you can see where I held it in the other gifs I posted here.