You think coding agents or models have not improved in 3 years? From my experience they absolutely have. I've spent a lot of time getting Claude Code to write clean features in a brownfield repo. I've gone from it helping me speed up to now Fable 5.1 doing it perfectly. And there are steps one can take to improve the quality which is to teach it (SKILLs) your important design and coding standards, as well as automatic design or code review to catch edge cases, performance issues, or whatever aspect you find a high priority.