Very good write up, as always, from Red Blob. It turned my high-level assumption on Google Maps pathfinding upside down. I thought, recalling algorithms class, that Google Maps worked so fast due to "optimal substructure" of shortest-path finding. That is that the shortest path from A-C through B also produces the shortest paths from A-B and B-C, and that for most of any given path you could route through some number of precalculated "midpoint" paths. Reading this turns it upside down in the sense that landmarks go behind the target, and not in the middle of the route! Very handy tool.
Yes, it's a bit weird! There are also optimizations that do what you describe, with landmarks along the way, but at least at the time I learned about it, road map pathfinding was using landmarks behind the target.