I honestly had no idea so many of those courses existed until I read this thread.
I get the point, I guess. I mean, grammar can be boring and can make you sound a bit too robotic, but it's also crucial to learn, so yeah I'd better learn some grammar if I wanna pick up a new language to study. Maybe grammar is less "important" in languages without any rigid word order rules, but I can't imagine picking up a language like German without learning a lot of grammatical rules.
So yeah, ofc one shouldn't only study grammar, but one shouldn't disregard it either. After all, most people who try to learn a new language want to sound rather decent at it, I'm guessing? Not illiterate. A lot of non-English speakers brag about having better English grammar than several native-speakers, after all. I think we've all noticed that. I'm only using the English language example because ti's the lingua franca. I'm sure it applies to all languages to some degree.
But tbh, it's also hard to think of or see grammar when thinking or reading or talking in languages we're very comfortable with. I feel that way with Portuguese and English. I remember as a kid always scoring high marks in English tests, even though I couldn't really explain grammar rules to you if you asked me. I just "knew" things by instinct, so I did a lot of tests in auto-pilot for the most part. Know what I mean? It's also hard to me to look at Portuguese from a grammatical POV, since I take things for granted, and even if I mess up obviously no one is gonna question my fluency; while a student of a foreign language will probably feel that way if he uses incorrect grammar and possibly even feel discouraged if a native speaker of his target language points that out to him in a condescending manner.