Instead of starting with a fat standard library, it started with minimal one and now each release adds 2-3 functions that could have been there in 2015. But none of it is idiom-changing revolution. These are mostly convenience functions, and you don't have to use them all just because they're there.
Every addition to the language is bikeshedded to death, goes through betas, revisions, refinements, before being stabilized years later. The first experimental release of async was 4 years ago and it has landed last November. So you may hear about new features a lot and they churn in nightlies, but actual big changes reach stable rarely.
Apart from async/await, since 2015 Rust made only 2 changes to how idiomatic code looks like (? for errors, and 2018 modules), and both of them can be applied to code automatically. I maintain over 60 Rust crates, some of them as old as Rust itself. All work fine as they are, and running `cargo fix` once was enough to keep them looking idiomatic.