I ran into the same headache—writing an OpenAPI spec and then keeping a separate GitBook in sync felt like twice the work. We ended up trying Apidog, and the biggest win was treating the spec itself as the single source of truth: push an updated spec and the interactive docs (with request/response samples, code snippets, etc.) update automatically. It checks most of the boxes you listed:

Imports/exports OpenAPI smoothly

Markdown + syntax-highlighted code samples

Interactive “try it” UI out of the box

Git sync + CLI for CI/CD deploys

Setup was basically “import spec → tweak theme → done,” and maintenance has been minimal since. Might be worth a look if you want to stop maintaining docs separately from your API specs.