I tried getting json deserialization into my app and ended up with a 2MB runtime, so it’s not going great.

Yeah sorry I meant Flutter ... 99% of people use Dart with Flutter, they are basically synonymous

I've been a professional programmer for ~20 years and worked in a variety of languages on a variety of different types of projects, and Typescript with Bun is mostly just fine. It lacks some low level primitives I'd like to have available for certain projects (e.g. Go channels), and the FFI interface isn't as nice as I'd like, but it's basically serviceable for for a very broad range of problems.

You should still know a language like Rust or Zig for systems work, and if you want to work in ML or data management you probably can't escape Python, but Typescript with Bun provides a really compelling development experience for most stuff outside that.

It is fine, though.

That's not a JavaScript issue. It's the same for almost any language where you don't use some bignum type/library. This is something all developers should be extremely aware of.