Most dependency management systems do that, but large projects often end up pulling multiple different major versions of (often very large) dependencies.

> 2) worse by forcing everyone to include the old deprecated dependency too!

Like I said I am no expert on Rust, but I assume that Rust can eliminate stdlib dead-code from the runtime? So unused deprecated features shouldn't be included on every build? Also deprecated features often are modified to use the new implementation under the hood which reduces code duplication problem.

> Bundling dependencies in the stdlib "solves" the problem by making new major versions impossible.

Yes, which is a feature. For example Go is very annoying about this not only on the stdlib. https://go.dev/doc/go1compat a lot of 3rd party libs follow this principle as well.

I bring Go a lot but I actually don't like the language that much, but it gets some pragmatic things right.

I am not saying everything should be in the stdlib, but I tend to think that the stdlib should be fairly big and tackle most common problems.