2-4 single use type definitions per endpoint sounds pretty atypical to me, but I agree choice of language helps here, e.g. TypeScript has pretty powerful typing

2-4 single use type definitions per endpoint sounds pretty atypical to me, but I agree choice of language helps here, e.g. TypeScript has pretty powerful typing facilities (Pick/Partial etc) that make type reuse far more practical. It's bookkeeping yes, but definitely not pointless.