The LLM is non-deterministic. You could have it independently do the conversion 10 times, and you'd get 10 different results, and some of them might even be wildly different. There's no way to validate that without reviewing it fully, in its entirety, each time.
That's not to say the human-written deterministic conversion tool is going to be perfect or infallible. But you can certainly build much more confidence with it than you can with the LLM.
This would require a robust test suite though.
One of the cases where vibe coding might actually be useful, writing a throwaway tool.
Should you use the LLM to do the thing directly, or use the LLM to implement a tool that does the thing?
I tend to reach for the latter, it’s easier to reason about.