This is how you lock yourself into a single front end design. And when you get ready for the next generation of your app or site, now you’re locked in and changing that front end design becomes exponentially harder.
In case of a complete redesign, yes you're right. With a generic API you will have about as much trouble writing the redesign as you did the original design.
In practice, a complete redesign is an incredibly rare event, and a good problem to have. Usually design of individual pages and layouts undergoes gradual, incremental changes, driven by real needs.
A redesign that requires front-end restructuring to such an extent that the data supplied is no longer sufficient should probably involve backend collaboration. Otherwise, you're tasking your backend team with building a generic site builder, which is much harder than a specific backend for your frontend.
In practice, a complete redesign is an incredibly rare event, and a good problem to have. Usually design of individual pages and layouts undergoes gradual, incremental changes, driven by real needs.
A redesign that requires front-end restructuring to such an extent that the data supplied is no longer sufficient should probably involve backend collaboration. Otherwise, you're tasking your backend team with building a generic site builder, which is much harder than a specific backend for your frontend.