Most software architecture diagrams are a mess ... partly due to ad hoc notation, and partly because it's very unclear what the boxes represent. C4 resolves the latter problem by introducing a small number of predefined abstractions. This sounds limiting, but the power of C4 is that limited set of abstractions, and the conversations it forces architects/developers to have.
This is a less prescriptive model than structurizr but keeps the goals of C4