That's what I was thinking with the "stupidly simple" comment. But I was thinking of my old golf buddy. He had no idea how screwed up his old putting alignment was. He'd literally be aimed 20-30 degrees right of his target. His putts were always in the general neighborhood of where he was aiming, but there was no way he could know if his putt was within 5 degrees of his original aim point. Pelz's bugaboo is that all normal golfers under read the slope and unconsciously compensate for some of the under read during their swing. The old version of this drill is to putt through two tees, but this gets tedious if you're adjusting the aiming point and is not as precise as using a line undeneath your putt. But that's not the point.
Good putters know that there are many combinations of aim points and speeds that can result in a holed putt. They are happy once they've found one combination that results in a holed putt. Great putters know that there is only one specific aim point and speed that has the greatest probability of a holed putt. They are happy when they've found the one aim point and speed combination that would have put the ball 17 inches behind the hole if it was covered. My buddy rarely made a breaking putt over 8 feet. He got really pissed watching me make more than my fair share of 10,15 and 30 footers. I wanted to help, but I had no idea where to start. I watched him switch to a long putter and that didn't really help much. However, when he changed his stance to hit the ball square to an aim point, his putting noticeably improved. This drill provides an explaination of why he was able to improve. It may not be right, but I'm buying it.
What struck me about this drill is that it first forces you to consciously putt along a specific line. If you unconsciously adjust the line of your putt, you'll bump the marbles/tees and remove that putt from the feedback process. Once this aspect of putting is removed, it becomes possible to pick an aim point and then adjust speed to find the speed that will put the ball 17 inches past the hole. Almost. Ideally, you'd do this drill with a "covered hole", but doing this drill to miss short of the hole less than 17 inches and long of the hole longer than 17 inches to set the aim point, then holing the putt to set the speed should work for setting the right aim point. Just picking an aim point and making the putt is not good enough. You have to change the aim point until your misses are the right distance past the hole. The concept here is that if you did this for enough different putts, you'd train your eyes to see the "right" break. The feedback/proof is how far you need to adjust your original aim point to the "ideal" aim point.
If you can't consciously read the green accurately, putting with an unconscious selection of aim and speed (aka feel) makes sense. But if the unconscious approach is not working well enough, this drill looks like a mechanism that lead to better results through better greeen reading skills. Given some of the comments in other threads on this forum, I was hoping that this idea would be helpful to other folks.