The operating test
A system is not successful because the diagram is elegant. It is successful when people can understand it, trust it, recover it, and improve it under pressure.
The best systems I have worked on share a few traits: they make state visible, reduce unnecessary choices, preserve context, automate recurring work, and keep risky actions explicit.
That usually means simple interfaces around complex internals. It also means documentation that is close enough to the system to remain true.