In working with DD on this drill and trying myself, i agree with the 'down to', and if 'no loop' means 'direct to the ball' then i also agree. I do not, however, agree with the imparting backspin. If that were the case the first step in the progression would not be possible. ie hitting into the plate.
I feel it as the wood chopping to start, hitting the ball square every time. Then each step out requires the body to get into a better posture to allow the ball to get farther while trying to make the same square contact. I don't think the drill wants you to hit under the ball to impart backspin, as if that were the case every step out would require to hit farther under to make the ball go farther out. As you attempt to hit the ball farther and farther on a line drive, by the time you are hitting over second base your posture should be pretty good, as the hands are still starting in the same higher shoulder position. The barrel needs to also start to get 'around' faster to meet the ball at the right angle to progressively hit the ball farther and farther. I see it as keeping essentially the same hand path (or at least the 'feel' of the same path) while getting the body into a better and better position to meet the ball.
We usually finish off trying to have her do the same thing but trying to hit bombs vs the liners over second. She has fun with it.
This has helped her not drop her hands to the ball , and be more direct because if the body doesn't move out of the way for the hands to get thru, the hands start doing bad things. I think.
FYI. Tewks also has a drill he calls the ladder drill. It's pretty similar in purpose.