API and system design is usually technique agnostic - but I think the biggest reason to have someone designing the system close to those doing the work is both

API and system design is usually technique agnostic - but I think the biggest reason to have someone designing the system close to those doing the work is both motivation and buy in. As people get more senior they tend to code less frequently, but that’s usually okay - a doc describing all aspects of a system is very much a coding exercise.