OTOH, flowcharts and such are still in widespread use.

Flowcharts and other types of diagrams are indeed in widespread use, but as design documents to be understood by humans, not as executable specifications. Being made to describe the high-level design of a system to humans, these diagrams are highly abstract and omit most of the details that would be required for an executable specification.

You can define executable graphical languages, as listed in the link I provided, but once you try to use them for anything but a toy example, your diagrams become excedingly large and complicated, essentially unusable.

And that a graph (mathematical sense) can be as precise as you like.

Irrelevant.