From my podcast on SRS I linked in another comment:
> [00:11:27] These SRS flash card apps are very good for learning vocabulary and depending on what's included in the flashcards, they could be for grammar as well. But the problem for a language learner is that it's de-contextualized. So say if you just study vocabulary words, then they're going to be a lot of things that you'll miss like collocations. You won't know which words are normal to use with which other words. For example, in English, if someone asks, "How are you?" it would be completely normal to answer, "pretty good". It would also be fairly normal to answer, "absolutely fantastic". But it would be strange to answer that you're doing "absolutely good". There's no grammatical reason. It's just not something that English speakers tend to say.
> [00:12:17] And there are many, many, many language features that are like this. There are also questions of word boundaries. For example, in English, the word "nose" refers to a person's nose or a dog's nose, but not every kind of animal. For example, an elephant in English doesn't have a nose. It has a trunk. In Japanese, the same word, 鼻 (hana), is for a person's nose and the elephant's nose. So the question is, what exactly does "nose" mean? Well, really tedious language teacher could explain this for every single word that you study, or even put this on the back of every flash card for every word that you're reviewing. But, it's not going to be efficient. You'll spend so much time worrying about edge cases for every single word that you're learning that you're actually not going to get anywhere.
Extensive reading avoids all of these problems. It feels slower than cramming words at the beginning, but over time, it's a much faster way to build a functional vocabulary.
I've since transitioned to rely on actual usage examples from books / in the wild. It's really the only way to actually learn, imo.
Else you'll learn that a word means "wide" but have no idea how to apply it. With usage examples, you train yourself to realize you might use this word to describe a wide road, but this other word to refer to a thick stick. And the correct word starts coming to mind in the wild, incidentally, without a deliberate step to understand the difference.
Definition alone is basically useless.