This is very interesting thanks for sharing. The PAC (presentation, abstraction, control) pattern helps explain a lot for me. That will certainly help in further understanding how the code is structured. I think tools like Movico can help developers like me coming from working in an MVC pattern understand what parts of Drupal correspond to what aspects of it's architecture. However I have to admit I have not been able to build a fully functional module in Movico maybe because as you alluded to it is forcing an MVC approach on a PAC architecture, or it could just be I need to learn a lot more.

Alex