that thing of the law of slowness is literally translated from Dutch to English, and I wrote with it that it's probably incorrect and I specified what I meant, but if you want a more accurate description:
Newton's First Law of Motion:
I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
Why wouldn't you punch higher if you just used weights? It's a proven fact that when people are in a room where gravity is lifted for a while, and they are asked to press a button for a repeatedly, each time performing the movement, and when gravity returns, they push below the button, and when they're used to that movement again, gravity is lifted again and they push above the button again. I just figured that'd be the same with a punch since you also extend your arm forward to a target, but it's possible punching is an exception, although I can't see how.