Grammatical texts are still useful for one thing. Self-assessment when a native speaker or some other teacher is not available.

A rational comprehension of a target language's grammar can accelerate production acquisition. What improves language proficiency is not raw mindless consumption or practice alone. But focused practice with a well structured intentionality. I've met my fair share of fellow language learners who can, for example, watch a whole anime episode without subs. But still can't produce a single word of original Japanese expression.

Can full on immersion produce language proficiency? Of course, eventually. Raw memorization is still not the answer. But eventually is not enough for most people. Study of grammar and guided exercises will reduce the time required to acquire language skills.

People who mix study modes still fare the best compared to those who rely on a single source of methodology. Yes, memorize words (in context is best, with example sentences). Yes, study grammar books (with a focus on practicing the concepts, not just memorizing tables). Yes, consume content (written and spoken) in the target language. Yes, find a learning partner. It can be the difference between being stuck in A2 for a decade and actually progressing over a couple of years.