I think you are close to the mark. There are ways to work in Java/JSP environment that is pretty quick cycle time. But I will say that our experience at PayPal is the code is more terse, less files, npm so much better than maven for managing dependencies, coupled with the fact that our javascript templating allows portability between server & client.

The Shift-Refresh style of programming is hard to overstate how much that creates a different mindset.

And to my point in the talk, the blending of prototyping and production tech stacks is also huge for being able to quickly iterate with users.