As well as your FE team forced to wait on BE changes for new features, you've also created busywork for the BE team anytime there's a FE refactor/restructure to boot.
An organisation that separates frontend and backend teams will naturally converge to an architecture where the collaboration between frontend and backend is minimized (i.e., a generic REST API) -- Conway's law.
This doesn't mean that an actual cross-functional team that contains both frontend and backend developers can't use the proposed single-purpose API to run circles around the split team.
This doesn't mean that an actual cross-functional team that contains both frontend and backend developers can't use the proposed single-purpose API to run circles around the split team.