In some ways, gradual or optional types give you the best of both worlds. You aren't obligated to submit to the whims of the type checker when you don't want to, but you can elect to get the safety of types where it matters. You can get the brevity of dynamic typing and the safety of static types.

But, in other ways, they give you the worst of both worlds. If you have any sufficient fraction of typed code in your program, then you will feel pressure to structure even the untyped parts of your program in ways that play nice with static typing. Some API design choices are more "typable" than others, and having static types at all discourages you from some interesting API choices.

In order to play nice with untyped code, most gradual and optionally typed languages are deliberately unsound. There are holes in the type system that can't be closed. That means compilers cannot rely on types for optimization purposes.

You end up with the rigidity of static types and the performance of dynamic types.