Anything can return anything and you only realize it at runtime is a massive headache. When you can't keep the entire code base in your head it becomes a liability.

I never used Ruby, but Python code bases love mixing in strings that are actually enums and overloading functions that accept all kinds of types. You just had to hope that the documentation was correct to avoid a crash.

Java 1.7 to Python feels very freeing from all the boilerplate. Kotlin, or any other modern language with a well designed standard library, to Python just feels like a bunch of extra mental work and test to write to just avoid brackets.