> In practice, back-end team tend to strive on "technical purity" and would ask the front-end team to take any hacks/workarounds necessary to deliver "compelling" user-experience.

The key is to design the DTOs (which API endpoints are based on) starting from the API consumer perspective. Business logic on backend is responsible to deal with mapping of DTOs to the domain models and in turn to data access layer models.

This results in most DTOs being "flat" and easy to consume by client.