Agreed that type-safety preventing training script failure is not the strongest argument for OCaml. In my experience, the far more compelling reason to use expressive type systems is that they allow you to be more specific about your domain models. This helps to not just prevent type errors (common but not that big of a deal) but also logic errors (I think more common, harder to suss out, and harder to catch with the equivalent amount of test coverage). This idea is often rephrased in FP communities as "Make illegal states unrepresentable."