It varies from project to project, but applications benefit a lot more than libraries. When I de-lib a normal express app it might add a few hundred lines of code and a few thousand new tests, but if I de-lib an library then depends on how ancient it is. The older the library is, the higher the chances that most of what it needs is built-in to the standard library.
Thank you. I have been thinking about the same approach. However my worry is the open source libraries often gets more eyeballs and CPU cycles and ends up much more refined over a period of time.