If you are in a completely self-defined world, then yes you can trust the compiler. But I once built a react component which was called from library code and it simply did not adhere to the method signature (this was for a material UI table extension).

As soon as you have third party code calling your methods all bets are off. It could be JS calling your methods, or there simply is a hidden cast somewhere.

This is the moment that you realize that type annotations really are just a compile-time fiction, much like Python. At least in my definition, this is weak typing as the variable is physically capable of changing to any type at runtime, despite its type annotations.