I think it would be helpful for this discussion to have clear definitions into what is waterfall and what is agile from a person on TPG.
Also, we have drawn this process as a line, and really it is more of a circle. There are places in the process that do not neatly check off boxes and then move to the next stage without going back and forth for a while. For example when building citations in VE, there were several concepts built and tested, and iterated, and tested (several circles, back and forths between parts of the process) until people were able to use it (it was usability tested and people were able to accomplish creating a citation without difficulty, considering all the details and edge cases), there were no bugs (this was a combo of QA and usability testing - which are different), then, it was released to production.
It might help to explain this process in a more visually representative way, showing that it really is a circle (we may some day decide to add functionality or remove functionality to the product called citations) that sometimes has circles (iterative testing until ready for release) within each part of the process. Drawn as a straight line with not back and forth between parts of the process (iteration), it communicates a less iterative process that does not reflect the reality of product development inclusive of the necessary activities to create usable, bug free, quality software. I think it is important to call out the back and forth between stages with arrows pointing backwards in the, at this point, unidirectional flow. Perhaps a visual designer could help us with creating a more representative visual to describe this concept.