>>> My take on swinging down has always been swing straight down like chopping wood until contact. That is the shortest distance to the ball and allows for more time to pick up a pitch. Once contact is made the bat stays in a level plane finishing level. I would never teach a hitter to hit the bottom half of the ball but to hit the ball "right on". Swinging down until contact causes a slight backspin on the ball and causes for a slight lift while hitting line drives. You should not continue your swing downward after contact is made. <<<
I hope you take my reply to your post as constructive advice. -- You will never reach your potential at the plate practicing "Swinging down until contact." For you to make consistent solid contact, the plane of your bat's trajectory in the contact zone must match the plane of the incoming ball. Since the ball in angling downward in the zone, your bat must be on an up-slope.
Matt, there is not a single MLB hitter whose bat is angling downward at contact. As the video clip below illustrates, their bats are all on an up-slope to match the trajectory of the incoming pitch.
High level swing plane