Genuinely curious, is the disappointment because it's limited to the JS/TS ecosystem?
My take is that by going all-in on TypeScript, they get a huge advantage: they can skip a separate schema language and use pure TS interfaces as the source of truth for the API.
The moment they need to support multiple languages, they need to introduce a new complex layer (like Protobuf), which forces design into a "lowest common denominator" and loses the advanced TypeScript features that make the approach so powerful in the first place.