The best codebase I've worked on was a 3D editor built using the waterfall method (written in Qt and C++).
Most of the engineers were above average.
Everything was planned carefully in advance and documented carefully, down to individual requirements. We even had some nice to have, optional requirements. After literally weeks of just documents and iterating on the architecture, the code for it was written easily in a week basically in auto mode - if we had AI agents back then we could have had the AI agents write the implementation.
During the implementation we realised there were some technical shortcomings (eg. number of lights supported by the engine) and clients wanted some changes, so we had to update our bible documentation and do a few changes. Some were small, some required to swap completely the rendering engine but we managed to keep everything to the same interfaces we planned at the beginning because the architecture was rock solid and we thought carefully about extensibility.
It may have costed more in engineering time than if we threw requirements on a kanban board and iterated on them - but then we would end up with arguably a worse architecture and no documentation.
Most of the engineers were above average.
Everything was planned carefully in advance and documented carefully, down to individual requirements. We even had some nice to have, optional requirements. After literally weeks of just documents and iterating on the architecture, the code for it was written easily in a week basically in auto mode - if we had AI agents back then we could have had the AI agents write the implementation.
During the implementation we realised there were some technical shortcomings (eg. number of lights supported by the engine) and clients wanted some changes, so we had to update our bible documentation and do a few changes. Some were small, some required to swap completely the rendering engine but we managed to keep everything to the same interfaces we planned at the beginning because the architecture was rock solid and we thought carefully about extensibility.
It may have costed more in engineering time than if we threw requirements on a kanban board and iterated on them - but then we would end up with arguably a worse architecture and no documentation.