Romanization is not used only for elementary language learners. It is absolutely required, as well as the standard, when it comes to discussing linguistic issues. Preferring one form of another depends on the type of question.
Also, it is important to recognize that hangeul is a 15th century script, which corresponds to Middle Korean. Prior to this is Old Korean, which is written in Chinese script. Old Korean includes sounds that no longer existed when hanguel was created, so it is simply not possible to write all Korean in hanguel.