They were half-assed in the sense that they trusted the old test suite, which turned out to be a mistake, as some edge-cases weren't covered. Hopefully they will be more rigorous going forward, but even then, these bugs were caught before being added to a stable release, so overall fine.
I'm not sure if it is the best ROI to rewrite battle-tested tools in Rust, but it isn't like people are forced to do it. People have fun writing Rust, and want to work with it more, so that's the direction these projects take. And if you don't want to use these tools, the beautiful thing about Linux is that if you don't like the direction a distribution takes, you can always switch.
I'm not sure if it is the best ROI to rewrite battle-tested tools in Rust, but it isn't like people are forced to do it. People have fun writing Rust, and want to work with it more, so that's the direction these projects take. And if you don't want to use these tools, the beautiful thing about Linux is that if you don't like the direction a distribution takes, you can always switch.