How grammatical abilities are acquired is still not known. This may be surprising. Probably, you have experienced this. You did drills, but you have never been able to use grammar, which shows that there is a big difference between explicit and implicit knowledge. One research shows that learners who were in an immersion setting acquired grammatical abilities. They mainly focused on messages or content rather than forms. If this is true, form-focused learning doesn't work. However, I believe grammatical knowledge is necessary to some extent. It is, for example, difficult to use the past perfect without explicit knowledge. I'm now reading "English Grammar in Use" published by Cambridge University Press. I'm sorting out grammar which I've been using subconsciously. I sometimes pick up some grammatical knowledge which I don't know. The point is whether grammar should be learned first or later. Later was better for me.