I think that having individual flow process charts of Zabbix processes and possibly other work flows as well would greatly improve understanding and developing Zabbix.

• From a developer perspective it allows a functional overview and to make logical tests of new or changed flows, without writing one line of code
• From a user perspective this reveals what exactly is going on under the hood without reading one line of code.

Although this would probably need a significant initial invest.
Nevertheless, I'm convinced that it pays off. Keeping the flow charts up-to-date then could be part of specification/development process and additional effort should be comparably low.