Dynamic Typing is like stuffing all your data into a pile of <String, Object>HashMaps and calling it a day.

It's fucking insane.

You lost all compile-time checks.
You will have to implement a million unit tests where a type system would have made these guarantees.
You literally have to find a way to exercise every single code path in your system in order to avoid the simplest of type mistakes. In this sense, you are forced to write exhaustive tests.
It's impossible, just from looking at a function, to know with any certainty what values are provided or generated.
Given a variable, it's impossible to know the valid range of values it may contain.