Comment by Timon3

You say that as if inexperienced devs would naturally drift towards doing data validation without TS, but that hasn't been my experience. Instead what I used to see were lots of unnecessary/repeated checks spread throughout most source files (and which frequently didn't catch the actually problematic cases), which I've seen much less frequently in TS projects.

Even without TS, I'd be using zod (or a similar library). I haven't had any issues with zod's bundle size, and I don't see a good reason to write custom encoders/decoders everywhere.