In Go, you solve problems by outputting inhuman amounts of code.
The standard library manages to pack a lot of functionality in little code. Its probably not easy to write simple concise code in Go but it is certainly possible.
The standard library is good. If you can solve your problem by mostly using tools from the standard library in a short main package, Go works well. The work that I do unfortunately doesn't have that property.
The point you are responding to is not about using th stdlib, but implementing it. If you look at the stdlib itself, it adds lots of functionality without too much code, from scratch.
Most of it doesn't. Take a look at net/http. I'm not aware of anything it does that your package could not. Certainly nothing that would move the needle on succinctness.
The std lib is disciplined about using safe Go ideas except in the exceptional cases. I feel like it’s nothing that is enforced by the formal spec of the language, just that the std lib has an exceptional emphasis on making it really hard to walk away with misconceptions.