I heard there are more works to clean up Rails codebases nowadays.

As of recently, I'm primarily using Java and I can say with confident that while it is old and boring, there are plenty knowledge sharing out there that elevates the brain of many developers (even by a small amount). Not to mention that the libraries have evolved in a much greater pace to support recent best practices (MVC, DB migration, unit-test, DI, mock, BDD, TDD, you name it, the Java community have them).