Secondly, there are many many advantages to learning vocabulary out of context. I am very interested in foreign languages, and have self-studied to elementary proficiency in Italian, German, and Russian. Memrise is my go to app for picking up vocabulary out of context, because it is the fastest path to a bigger vocabulary. For a lot of vocabulary, at least for the languages I've come across so far, there is a direct one to one mapping for the essential things.. E.g. you can learn the word for "book", "fire", "box", "sky", etc. out of context. Certainly, learning in context has advantageous for improving grammar and in some situations verb usage - therefore a more balanced approach. An easy example of the advantage of in-context language learning is that in German and Italian, knowing somebody uses different verbs than knowing a thing. If you were to study a verb like "to know" in Memrise, you rely on the flashcard's definition to be thorough enough to clarify their usages.
[0]: "A Trainable Spaced Repetition Model for Language Learning", writes about how spaced repetition is used by Duolingo. https://s3.amazonaws.com/duolingo-papers/publications/settle...