I like go's library it's got pretty much everything needed out of the box for web server development. Backwards compatibility is important too.
For stuff in the standard library proper, the versioning system is working well for it. For example, the json library is now at v2. Code relying on the original json API can still be compiled.
At least it is my experience building some systems.
Not sure it is always a good calculus to defer the hard thinking to later.
Rust on the other hand has "log" as a clear winner, and significantly less overall fragmentation there.
But this does more than just add a maintenance burden. If the API can't be removed, architectural constraints it imposes also can't be removed.
e.g. A hypothetical API that guarantees a callback during a specific phase of an operation means that you couldn't change to a new or better algorithm that doesn't have that phase.
Realize the "log" api is bad? Make "log/slog". Realize the "rand" api is bad? Make "rand/v2". Realize the "image/draw" api is bad? Make "golang.org/x/image/draw". Realize the "ioutil" package is bad? Move all the functions into "io".
Te stdlib already has at least 3 different patterns for duplicating API functionality with minor backwards-incompatible changes, and you can just do that and mark the old things as deprecated, but support it forever. Easy enough.
Is that 'supported'? A library that uses a callback that exists in 'log' but not in 'slog'; it'll compile forever, but it'll never work.
'Compiles but doesn't work' does not count as stable in my book. It's honestly worse than removing the API: both break, but one of them is noticed when the break happens.
Letting an API evolve in a third-party crate also provides more accurate data on its utility; you get a lot of eyes on the problem space and can try different (potentially breaking) solutions before landing on consensus. Feedback during a Rust RFC is solicited from a much smaller group of people with less real-world usage.