The idea that language acquisition is about consciously learning rules and applying those rules has been debunked a long time ago.
Despite that, a lot of people today still approach language learning this way.
There's a massive amount of evidence showing that we do not acquire languages, whether it's our first language or a second language, this way.
And we already knew this in the '60s and '70s.
So a lot of people today learn a language as though they are still stuck in the '50s or something.
This doesn't mean you cannot learn a language using outdated methods.
People in the past did learn languages.
It just means that if you use massively outdated methods (there are several popular methods from the past), it will be pretty inefficient, because those methods are based on a false idea of language acquisition.
Again, you can always learn something from something, even if it's not super efficient.
But once you update your knowledge, skills, and approach a language in a more informed way, you can see how much faster you can learn a language to a conversational level (not to perfection, though).
This doesn't mean there's one specific "correct method".
If your general direction is solid, there are many different things you can do and many different resources you can use based on your personal preferences.
Communicating this can be a little hard for beginner language learners, because they often have a preconceived idea of how one should learn a language.
But once you experience how quickly you can acquire a language to a decently conversational level, you can see that a lot of people are taking an unnecessarily long route to reach their goal.
At the same time, I do acknowledge that outdated methods can have "psychological" benefits for certain learners because they give you conscious knowledge of the language, which some people find reassuring.
Language learning is largely an unconscious, intuitive process, which makes measuring progress not very straightforward.
So consciously learning rules, even though it's not the direct way of acquiring a language, can have psychological benefits for certain learners with certain personality dispositions.