If you think about it, even if your swing is level your arms and bat have to start coming up as you enter into the follow through. The follow through almost always brings the bat up to around shoulder level. Unless I misunderstood him, his technique was to get a batter to hit the ball closer to the point when the upward part of the swing takes place. So the batter can take a level swing, but if he makes contact 2 or 3 inches more ahead of him (because he is standing back a bit), the natural trajectory of the follow through will give the ball a slightly higher launch angle. At least, that is how I understood it.
Philip (TP) may have more technical insight into the mechanics of the swing.
The reason they use tee balls is to create a level swing but at this point I am unsure what that means
It probably means you are not chopping down with your swing not that you cancel out the natural raising of the bat in follow through
If a home run hitter swings early to hit the ball on upswing he has less time to react to curve ball etc which makes him strike out more
A side note is I got into a cage and the ball was 80 mph. About the speed of finesse pitchers
I could not hit one. The owner used to be a pro and told me I was hitching my arms before swing, With that one tip I then hit every pitch. But they were all grounders
I asked him why and he said I needed to level out my swing
I think he meant stop chopping down
technique in sport makes all the difference
Natural athletes do it without thought the rest of us have to learn