You can make the macro smaller/faster by replacing the two subtracting combiners (I only noticed I've spelled "subtract" wrong my entire life) with a single combiner in Min mode.

It becomes clear if you draw yourself a quick sketch.

(At a point, where the height x of the blurred heightfield is less than the height h of the original heightfield, your macro does this: h-(h-x), which can be reduced to: h-(h-x) = x)

Unfortunately, the macro seems pretty trivial now. Your current method would also cut off "spikes" that are only small hills, thus removing the details on these.

That being said, maybe that method can be improved to select spikes in a more clever way, pushing that select and subtract approach, which is a very effective one for many purposes

edit: maybe only subtracting spikes that exceed a certain height