(article author here) There's definitely nothing wrong with Mermaid. In fact, the current syntax at https://flowchart.fun can be converted to Mermaid (in export window) and I'll continue to support that when I migrate the app to the new syntax I'm proposing in this article.

The biggest differentiator is indenting to create edges, which I think is useful for some graphs and in some contexts (especially for quick brainstorming). Mermaid is great and super expressive.