Prompt coding is more expensive than programming ?

I have been writing code with Cursor and claude code since last 8 months,
It has been a smooth ride for projects built through prompt engineering with well documented prd and agile development docs ,But for pre-existing codebases ,particularly the frontend applications even when they already written which are documented at an architectural level, it becomes too iterative and expensive for claude code and cursor to refactor the code with incoming problems of claude code or cursor stuck in the circular loop because of no context of inter-dependencies of modules .