In a nutshell - Scope and first things
Fair enough Ruth --
I'm not querying the content integrity of the selection of diagrams -- but rather the formats in which diagrams are created and stored. Sourcing existing svg graphics means that we can save time, energy and money - moreover, they can easily be edited for alternative scenarios.
Like I said -- I have no expertise in your content area - just trying to give a few tips on how to improve the productivity of your content development processes in a contemporary environment.