IMO the opposite is true; without types you give up some developer productivity in the form of time spent writing tests and debugging issues that the type system would obviate automatically. In my view, loose typing adds the illusion of productivity because the developer might presume they are working faster because they don't have to reason about type restrictions, however they simply end up enforcing type restrictions manually (and relatively poorly compared to a solid type system) using "typeof" and "instanceof" checks throughout their code. In general, assigning multiple types to the same variable is considered a code smell anyway, so strict typing simply enforces what is already considered a best practice.
Of course, this doesn't mean that choosing typescript in particular is always the right engineering decision, but, all other things being equal, a strict type system is almost always preferable to a loose one.