My big complaint about mermaid is that you cannot easily generate and store the SVGs without a browser engine—-even the CLI goes and runs Chrome, which feels insane.
Regarding graphviz/dot, I have been using it from what feels like the dawn of time and am somewhat sad that we haven’t improved upon it. The syntax, styling imitations, etc. put me off enough that I tend to avoid it.
For graphviz, the "problem" with it is that it truly is general purpose and trying to make a general purpose syntax for diagrams is difficult. Mermaid tackles this by not having it be applicable to all possible graphs (flow chart has a different syntax than gitGraph) allowing for a better domain specific language for each subset of functionality.
https://mermaid.js.org/syntax/packet.html is really neat... and it would be a pain to do that in GraphViz ... but I believe that's more of a demonstration that it might be better to do specific syntaxes for specific types of diagrams.
Regarding graphviz/dot, I have been using it from what feels like the dawn of time and am somewhat sad that we haven’t improved upon it. The syntax, styling imitations, etc. put me off enough that I tend to avoid it.