The issue with not having something deterministic is that when there's regression, you cannot surgically fix the regression. Because you can't know how "Plan A" got morphed into "Modules B, C, D, E, F, G," and so on.

And don't even try to claim there won't ever be any regression: Current LLM-based A.I. will 'happily' lie to you that they passed all tests -- because based on interactions in the past, it has.