[mercurial]

Well, an order of magnitude of difference is a hint that, whatever the quality of the existing crates, there are definitely areas for which you are going to be hard-pressed to find a good solution (say, localization), or a solution at all.

It is not a sign that there is anything wrong with the Rust ecosystem, it has a very active community and things are moving in the right direction, it is not just as full-featured as more mature ecosystems out there.

See for instance https://github.com/ErichDonGubler/not-yet-awesome-rust

There are quite a few use cases not listed here, obviously.