Personally I never struggled. You can employ interfaces and maintain them judiciously.

But interfaces are informal. Not using a monorepo say makes it harder to be sure if your broke downstream or not (via downstream’s unit tests).

But freedom from Rust’s orphan rule etc means you can decompose large code into fragments easily, while getting almost Zig-style specialisation yet the ease of use of python (for consumers). I would say this takes a fair bit of skill to wield safely/in a maintainable fashion though, and many packages (including my own) are not extremely mature.

I personally think it requires discipline, I saw it go both ways.

I was never an expert in the language, but worked along people who were and they generally made nice code.

But there were a few places where I saw intensely confusing patterns from overloading with multimethods. Code that became hard to follow, and had poor encapsulation.