It has nothing to do with upfront waterfall design specifically. Making choices about how you represent information is an integral and unavoidable part of algorithm design at any level of detail.

There are no projects for which a certain amount of thinking before you write is ill-advised.

Indeed, and personally I find that having the types around also makes it much safer to do the inevitable rounds of refactoring once you figure out what you're really building. (Especially in a language like Haskell where most of the type information is actually inferred from context. It requires absolutely minimal type annotation.)

EDIT: Maybe it's just my bias, but it seems to me that most of the "dynamic" crowd just haven't tried a truly "agile"[1] statically typed language like Haskell or O'Caml.

[1] Hey, if they want to abuse the connotations of out-of-context words to describe the paradigm, so can I. :)