Agreed and for a few years now that's what I have done. But for detailed, log/debug driven sequence diagrams that often required parsing a log, generating a compliant text-input to the tools followed by submitting to the tool and exporting the graphic. This 30-minute project is a step in the direction to fully automate the process.
That's an excellent point.
While we should reach for prior art, something like this bit of python is good for the hip pocket for those moments when PlantUML might not support some zany requirement.
for more sophisticated scenarios (or customisation), you can still get "rendered from text on my computer" using tools like PlantUML. (Or GraphViz for graphs, etc.).
Embedding the resulting diagrams in the text editor (like Emacs' org-babel allows for) makes for a nice diagramming experience.