I don't get some of this. Consider just a plain side hill putt. You could aim and putt for the highest part of the putt''s line to be 2' above the hole, or 3' or 4' or 6' or 10'. You have to have perfect pace on any of those to hole it.
If we start with the basic premise that we hope to start the putt on the line we aim the putter, aiming the putt for the highest part of the putt's line will absolutely guarantee a low side miss every single time on a breaking putt. If the apex of the balls path is 2' above the hole as it rolls into the center of the cup, the actual aim (starting line) of that putt is significantly higher than 2'. "Perfect pace" is nice, but no one has perfect pace every time - there is a window of pace that will still hole a putt on a given line. The idea on pace IMO should be to have the hole play as wide as possible to "catch" more putts... that's the pace I prefer to putt with. But whatever you own personal target delivery speed is, that's your baseline for the amount of break you play and the determinant of how big your "window" is.
I putt this video together a few years ago for someone. IIRC, it's a 10' putt with the ball rolling at an apex of about 6" above the ball-to-target line (a straight putt). Let's say you are the one making that putt out on a real green, and your playing partner is next to putt be he's just inside you on the exact line. If he's paying attention,
he sees the ball break about 6". If he's like most golfers, he lines his putt up and plays 6" of break (the orange dots). He starts it dead on his aim with the exact speed you used, but look how badly he missed. 99.9% of the time, his comment will be "I pushed it" because the ball never got 6" high and he missed well below the hole. The problem wasn't a push, it was that this putt had to be started on a line that was roughly 12" outside the top edge of the hole to make it just inside the low side of the cup.
No one intentionally chooses to make a putt in the low side of the cup, so you could've actually started this putt 14" above the top edge (for a center cup make), or even 16" above the top edge (for a high side make). So for the speed this putt was rolling, there was an effective 4" of break window that would have most likely still made the putt. That's a pretty good sized window for a 4.25" hole.
How is knowing it's a 5% slope and the green's speed (and where the fall line is) going to help you choose the combination of aim and strength which for you on that hole that day will lead to you actually holing the putt (if that is your destiny)?
Knowing the speed creates your baseline. Being able to identify or recognize what a 1%, 2%, 3%, etc. (5% is pretty drastic and the pin placer should be hit in the nuts) looks like begins telling you where you should be starting the putt in relation to the fall line. In the putt above I knew the slope and speed before I started setting up the "putter" and his aim. The only trial and error part of this putt was learning how far up the slide equalled what speed.