If you already know what the inputs/outputs are, why should you spend days or weeks of your life typing it out rather than giving it in a well-specified and tested form to an LLM to get it done a hundred times faster?
Those costs don’t disappear and it’s truly naive to think they don’t matter. Take security issues, they may arise because what you thinks was the input is merely a subset of the true input range. And the extra possibilities lead to unforeseen behavior.
A lot of programming is about ensuring that the input and the output are the sets defined in the specs. And the rest is that the transition/relation is the right tradeoffs of performance, correctness, and costs.
So, code?