I find Mermaid's syntax difficult to use and understand past the simplest examples. I've also run into some strange edge cases with it, but can't remember the details right now.
Is there a way to get a git diagram out of D2? It does have nicely streamlined syntax.
One thing that worries me is that the profusion of text-based graph description languages will result in a family of software that's unparseable due to its success. We have Graphviz, GNUplot, PlantUML, BlockDiag, Mermaid, Kroki, Vega, and too many others to count - but we don't have a Pandoc.
Out of these text-to-diagram tools, D2's syntax seems the friendliest to me. See https://text-to-diagram.com/.