> f I have a rich object in a debugger in Python, I can call dir() on it to immediately see what I can do with it. Whereas if it's a simple dataclass, I'd need to search through code to find how I can use it.

No OOP language can have a search feature as useful as Hoogle:

https://hoogle.haskell.org/?hoogle=%5BMaybe+a%5D+-%3E+%5Ba%5...