It depends on the complexity of the problem. Data classes can make the code easy to read, and if you use a good IDE then it will also be faster to write.

I suggest you focus on making the program work, before considering how to best manage state. Readability and performance can be improved through refactoring later.

I agree, good point.

I was just trying out something in a game, and minimizing mutable state has lead to some interesting ideas. Not to mention that it trivilized creation of custom data types.