I really enjoyed the few minutes I spent with it, and I've got it bookmarked for the next time I want to visualize a large number of tasks and requirements! Your described use case of "project tasks dependencies" particularly struck a note in my head.
Anecdote: part of the initial hook in playing with knotend (i.e. fun) was trying to infer the key mappings. I didn't end up checking out the demo.
Regarding the larger picture of "diagrams for stuff", my own take is that it's a realm that one tool can't cover all use-cases. As an exercise, I started listing some of the broad use-cases and my go-to tools for them...
- simple (simplistic often) for presentations - where refined tweaking is key (Lucid chart, previously Inkscape)
- large, autogenerated - "I'll trace the flow, it just needs to be sane" (graphviz)
- structured customized, small/medium flow charts (yed/plantULM in the past, next time probably mermaid)
- gantt charts or other task dependency trees... these are like the "project task dependencies" you wrote of, but with a time aspect added in... (I don't make these much...) It seems like tools are likely to do gantt or flow charts well, but not both.
- nested text lists (not really a flow chart, but a common way of organizing my thoughts)
- flat lists (not really a flow chart), how I often dump large lists of todo tasks for projects. (I like using google sheets for this; I just wish I could drag and drop rows)
Having bumbled my way through listing all of that: I was going to ask if you think knotend is still on the path to being a general-purpose flow-chart editor... but then realized you specifically talk about "graph editor", and I have not formed opinions on that topic. So I don't have a question here really ;)