This does not reflect my observations at all. It works if you’re an end user and the software you want has been packaged. But if either of those is not the case, you’re left in the mud. Rather, you end up with builds that are difficult to set up or reproduce except on specific platforms, require a lot more maintenance over time because bitrot occurs naturally (your code depends on libexample 1, but Debian only package version 2 now, so good luck dusting off that project you made five years ago and getting it to build again), vendoring upon vendoring, more diverse and generally lower-quality dependencies for a particular task, and other problems like these. You’ve solved one problem, but at a very significant cost that must be acknowledged, even if you decide it’s still worth it.
Take an app written five years ago that depends on majorish C++ libraries, and there’s a fair chance compiling it will be a nightmare and require invasive surgery due to version incompatibilities. It’s not improbable that the most pragmatic solution may be to find and rebuild the transitive package tree for some older version of some package, and that’s generally quite painful (and can be outright incompatible).
Take an app written five years ago in pure Rust, and it’ll almost certainly (p>0.99) still work fine. Take an app written five years ago in Rust that binds to some C/C++ library, and there’s a fair chance you’ll run into trouble, but it will almost certainly be a good deal easier to resolve, much more likely to work with only a version bump and no other changes than in C/C++.
As a developer, I know which general mode of operation I prefer. Debian are welcome to twiddle the dependencies in the way that suits their chosen requirements, but the canonical sources are still crates.io, and I know that when they’ve stopped packaging example-1.0.0, I won’t be beholden to their packaging but can just use `cargo build` and it’ll still work (contingent upon extern bindings).
I’m dubious that any meaningful curation is happening, and curious if there’s even cursory review of crate contents. But most of all, I’d be interested in a statistical comparison of the crates that Debian ships with the most-downloaded crates from crates.io. I suspect the sets would look very similar.