Are my one-method (and a couple attribute) classes overkill?
You are correct - in this case classes are an overkill.

Think of classes as nouns, and methods as verbs. Functions do things, while classes are those actual things.

For instance - compare DataFrameBuilder (noun) with build_data_frame (verb). Which makes more sense? Which describes the business logic better? I think the second, since the focus here on building data, and not on a builder itself.

I think I picked up the idea from Steve Yegge's post "Execution in the Kingdom of Nouns" (great article, you should read it when you have time).