Toly, I majored in math in college, and I disagree with pretty much every comment you've made about tennis strokes. Most of your comments seem to be about how players are wristing their grounstrokes, and vectors can prove it somehow. I think If anything is happening with the wrist at the end of the stroke, it's because of the preparation that happened earlier. In my mind, players have relaxed, fluid strokes, and their wrists are relaxed at the end. I'm not sure how vectors fit into all your wristy groundstroke arguments.
I question whether you understand even basics concepts surrounding vectors. Most of your posts on technique are so off the wall, then you will draw a vector and claim it somehow supports your post. I'm not seeing the connections.