That concept map example is only a loose association of ideas, where the nodes aren't of the same type (e.g. event, state, class etc), or sorted into types, and apparently included quite arbitrarily. Mind maps are similarly loose. UML is for when you want more precise diagrams about a fixed subject matter.

I agree on the "shorthands", like empty/filled arrows, that people may not know. But there isn't much alternative to such shorthands other than leaving them out completely, which wouldn't be an advantage. In diagrams some information is either conveyed succinctly or not at all. The "alternative" is a block of text instead of a diagram.

That's heavy backpedaling from your earlier

> People who say "UML is useless" basically say "diagrams are useless".

Well, if you only allow concept maps and mind maps, then I guess, yes, you don't actually say (all) diagrams are useless. But you are pretty close.

Not exactly related, but this concept map looks amazingly similar to a semantic ontology. RDF/OWL may not be the easiest encoding, but is quite capable in organizing very large concept schemes.