The greatest thing about Graphviz is indeed the dot language. A nice thing about using dot is that the graph definition is *portable among all applications that support dot*.

Dot is such a simple and readable format (particularly if using the basic features). Thus, it can make a ton of sense to define graphs in strict dot, even if you will be rendering with another tool than Graphviz.

These days, there are other popular options, too -- Mermaid, etc, as TFA indicates. Nonetheless, Graphviz/dot will remain for the long haul, IMO, because dot is so, so good.

So, you need Graphviz for its syntax definitions primarily, and because it is a standard that could be recognized/run anywhere.