The point remains, though, that I avoided an unnecessary dependency. I copied that function once and never needed to mess with it again, because it was 15 lines

The point remains, though, that I avoided an unnecessary dependency. I copied that function once and never needed to mess with it again, because it was 15 lines and I could verify personally that it did what it needed to do. For contrast, we wanted to be able to incorporate new versions of React, because it isn't a simple enough thing that it can be written once and be done. It evolved, and offered real improvements in terms of performance and useful features. As in all things, there are costs and benefits to making something an external dependency or not. The key is to realize that there are indeed tradeoffs, and that outsourcing every single thing you can isn't necessarily ideal.