The diagrams as code is not a one size fit all. I'd use mermaid for some technical things, but it's failing for communication/presentation purposes. You need to have the ability for arbitrary placement, annotations, flow. Mermaid is all fun until you want to connect two previously distant boxes and everything explodes - for long-term documentation purposes it may not even matter, but if I'm about to show it to anyone, I'm going to Excalidraw.