Development should never be broken, ever. Ready to ship and broken are two different things. By ready to ship it more like v2 has 8 total new endpoints and only 2 are ready, then 4, then 6, then 8.
When the tests fail, or the code quality goes down, the deployment fails. I would rather have DEV broken than PROD. Not sure how going directly to PROD would make anything better in this scenario. That is what Integration is for never broken always ready for promotion to prod. Plus a few broken dependencies means ‘yellow’ === impairment not unusable. If the app is unusable for any one dependency that is another issue.
Mocking data when you are ahead of another team is always the reality…