Sure, runtime validation is useful – at the boundaries of your domain! After that your type checker should ensure your data has the shape your code expects.

In other words: Parse, don't validate. https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-va...

Yes

The boundaries of my domain is everywhere, because stuff are built everywhere. I'm sure I am a bad dev, yet prebuilding all possibles objects I might need everytime I receive an input sounds stupid at best

(btw, this post sounds a lot like "if it compiles, it works", not gonna do this, especially in Python)