When I originally submitted the issue I hadn't finished going through all of the dataclasses code and it hadn't even occurred to me that it could be valid to use ClassVar with field(). I (wrongly) assumed this would always raise and that field() is only valid for things intended to be instance vars.
I do find this behavior a little surprising, but on reflection I don't think it's explicitly wrong as long we raise for default_factory like it currently does. I think it's then appropriate to just do the exact same behavior for Final as ClassVar.
I'm going to start working on a PR, thanks for your feedback.