Also not necessarily with third-party libraries.

True! Although it’s easier to swap out a third party lib that’s using a bloated dependency than it is to avoid something in std.

Indeed. However, you need to recognize that having those features in stdlib creates a huge bias against swapping them out. How many people in Java actually uses alternative DB APIs than JDBC? How many alternative encoding libraries are out there for JSON in Go? How about async runtimes, can you replace that in Go easily?