> The design was in my head, and with hindsight I could see all its flaws. I was therefore able to [re]create a much more efficient and effective design based on that learning. All the mistakes had been made, so I was able to get this version of the code right the first time.

Notice the critically important difference of recreating an existing design, vs using the rewrite as an opportunity to experiment on the design and the implementation (and the language, and the ...).

Vetting a new design takes time, consensus, and subjective judgement. Re-implementing an existing design is laser focused and objective.