Interesting insight on the freedom of downstream issues allowing one to become aware of upstream issues. I suspect there is some truth in that. In closed chain movements (where you move your body around a fixed limb, like the squat), the mobility issues furthest downstream will be the first to throw off your pattern. If your ankles are tight, they will automatically block any squat pattern that demands a significant amount of ankle dorsiflexion (knees forward). If your wrists are stiff (you’re missing extension), you’re going to have a hard time even getting into a good position to start a push-up.
But I’d say this probably only holds true in movements that demand a significant range of motion contribution from distal joints. For example, even a slight ankle restriction will make the overhead squat a nightmare, but you can get away with it during the back squat and have no issues, because there is much less ROM demanded from the ankle in this squat iteration.
I think the more general rule of thumb would be that your greatest restriction in a given movement will be the first restriction to limit your performance. Let’s say my ankles are 5/10 stiff, but my hamstrings are a whopping 9/10 set of steel cables, my hamstrings are probably going to present the biggest roadblock, and therefore the restriction I should target principally in my movement prep.
Go for your biggest issues first. Upstream and downstream will guide your search, but clearing your most heinous restrictions is how you will get the best ROM payout.
Also, gotta emphasize again, restoring range of motion and achieving the oh-so-coveted suppleness of the leopard is not an all-or-nothing, overnight battle. You have to see mobility as just another facet of your training, every bit as important as your strength and condition, and underscoring every movement you make. It’s very important, but it takes great time and consistency over that time to make real change and restore normalcy. Have patience, take the small improvements as they come, and recognize that this is just as much a long term journey as getting stronger, faster, and more skilled is.