Designers of atproto actually agree with you so the data is not unstructured! It’s structured by schemas (called “lexicons”) controlled by app developers.

Data in user repositories is treated as untrusted input by apps, and rejected if it doesn’t pass the corresponding schema. Schemas are evolved in a backwards-compatible way with a nudge towards future extension (eg open unions are default).

That’s exactly why you can’t make a 500 character post on Bluesky. The Bluesky server will ignore your record as being invalid.