stdx is not the best example. The most popular package that is not on crates.io is probably embassy.

Also Debian tries to build and distribute independently from crates.io.

So crates.io is important but is not the (Rust) world.

There's no single "embassy" crate, but all the components (HALs, executor, usb, net, etc.) are all on crates io and have been for a long time.