Tree-shaking isn't a sophisticated feature with ES2015 modules and it's more surprising today when build chains don't support it. (The sophisticated features come into play doing any sort of tree-shaking on older module types such as CommonJS or UMD.)

It's not even a build-chain only feature at this point. Some of the reasons the ES2015 module format was built the way that it was were exactly so that browsers can do their own tree-shaking of runtime code. Even if you don't save on the performance impact of the extra 30 KB from being downloaded, in modern enough browsers you would potentially still see a performance impact on browser memory usage and JIT compilation time.

Even if your bundle size has bloated to a MB already, a 30 KB savings is still roughly a 3.3% savings. It's still noticeable. Whether that is "significant" is an argument of personal taste and how many "9s of performance" you try to deliver. Even single digit percentage savings can be huge "significant" wins for many projects.