Parcel is a rare thing in the JS world: a tool I’ve actually found useful and efficient. As a bundler, it does indeed do a lot of things correctly out of the box, and as a direct result the experience of using it is far more pleasant than most such tools.

However, it is also a tool for one job: bundling. If you also want to do things like unit testing or running any sort of linter or style checker over your code, you probably need to figure out how to get those tools to read your TS or ES20xx code as well. You might still need a handful of additional libraries to implement your test suite. You might still need to configure your preferred style and which rules you want to enforce in your static analyser(s).

So even if Parcel was flawless about installing what you needed for your dev and production builds automatically, you’d still end up needing to install a bunch of other tools and write a bunch of other configuration files. The overall efficiency of setting up a realistic development environment, even using Parcel, is still limited by a kind of Amdahl’s Law problem.