2019, I read the tweets but I don't see an explanation of why/how it would be meaningless. Can you explain it to me?
In my simple mind... we all know that a pitch thrown from a regulation mound at velocities and spin rates that are currently being achieved cannot actually go uphill. So, the options are something close to flat or something more downhill. With consideration to the strike zone and typical size of most hitters, if a P keeps the ball in the lower half of the strike zone and has a plane that is noticeably downhill, a hitter will have more difficulty putting a good swing on that pitch that keeps the barrel on plane for any length of time as compared to doing so on a pitch that has a flatter plane. Yes, he can match his swing plane to the pitch but it requires him to first get the barrel further below the ball before getting it on that steeper plane. So, timing and execution are more difficult. Add in perception of the hitter and it only compounds the level of difficulty.
What am I missing? I am always genuinely open to learning.