Whoah, hold on there, I disagree entirely. Modern optional type systems are great for incremental development, as I can ignore them for the most part in my code when rapidly iterating, but then when my APIs are starting to solidify, bring in some proper guarantees about my code's correctness. I've used Hack and TypeScript in production, and while they're no Haskell in terms of "moderness" of the type system, they're both quite nice.