No one is talking about abstract type theory; we’re talking about the intuition you use to write maintainable, correct software including CSV munging.
In general I know what you mean though. “What if this CSV parser turns out to be really important?” If you think there’s a high probability of that, do it in a statically typed language then. 99.9% of data munging I’ve done have been throwaway programs to answer a question to inform some decision or help refine a mental model.