In my experience, static typing takes a different way of thinking that can take a while to get the hang of, and during that adjustment period a lot of people are going to significantly slower. I definitely felt it coming into Swift, being used to Objective-C and to a lesser extent Ruby.

Having grown accustomed to static typing, not encountering errors until runtime, or worse having errors manifest as type-related misbehavior and potentially not be immediately apparent is much more frustrating than it used to be.