Problem is, there’s a well known principle of library design: any behaviour you exhibit eventually becomes something someone relies upon. You can choose to live with silent breakage or you can validate your inputs within an inch of their lives. Next, with the best will in the world, even with a small library, you quickly discover a wide range of use cases that should reasonably be supported by your library. So all libraries end up complex, not just because of validation.

Yes, static typing would help with some of this, but very much not all.