I'm in the middle of moving my app to openAI structured output.

Could you please explain what you mean by "which everyone moved on from"?

Structured decoding limits next-token probabilities to ensure valid JSON. The main issue is that if the model puts a substantial probability on an invalid token, then it was already confused, and in that case, you don't actually want whatever the next-most-likely valid token is: even if it's syntactically valid, it's likely semantically erroneous.