I definitely have made decent use of Mermaid diagrams in GitHub. But Mermaid diagrams are hard to layout, and there is only one experimental layout that's good for automatically generated diagrams. It's nice, but it's not quite there. I have tended to bounce between Mermaid and Visio.

I'm generally not a fan of exporting and importing diagrams constantly. One thing that is nice is that Confluence can support plugins for diagrams, which is okay-ish.