Targeting OpenAPI 3.0 is a bad idea. It wasn't until 3.1 that it became truly useful, if only because it fixed one glaring blunder: Pre-3.1, you inexplicably couldn't provide a description along with a $ref. This defeats one of the major purposes of OpenAPI, which is... documenting your API.

Example: If you define a structure called Rectangle and use it all over the place, you can't say what this rectangle means or that rectangle means when the structure is used in your API. How was that ever deemed acceptable? Widespread use of common structures (which one would certainly expect in a well-designed API) resulted in an API that couldn't be documented in OAS.

The OpenAPI code-generation landscape is truly abysmal. Not only do almost none of the tools support version 3.1 (which has been current for years), but the generators themselves are of widely varying (but mostly shitty) quality and scattered across a couple of apparent major repos. The documentation is likewise a confusing morass of conflicting and incomplete information from several sources. I flailed away trying to fix one generator for weeks, or write a new one. But I couldn't even find a concise list of the data structures offered to the template engine after an OpenAPI doc is ingested by OpenAPIGenerator. Isn't that a fundamental part of creating a new generator?

So it raises the question of whether OpenAPI is salvageable, or whether this new DSL is better... from design to code generation. Given the trashy state of OpenAPI code generators, why bother generating OAS at all? Just move on and write some competent generators using this new language.