A similar line of thought made me think about the usefulness of apps like Duolingo. People who learned languages back then did it with textbooks and most seriou

A similar line of thought made me think about the usefulness of apps like Duolingo. People who learned languages back then did it with textbooks and most serious learners still do. Do we really need new methods other than spaced repetition (of which software is a slightly more efficient version of flash cards)?