The power/guarantee trade off isn't a fundamental one, even though in current languages you often have to choose between the two. Creating languages that combine the power of untyped languages with the guarantees of static languages is an active field of research. For example, dependently typed languages, while currently too unwieldy for everyday use, show promise of having both power and guarantees much stronger than Haskell. Now a third, ill-defined axis of "usability" comes into play.