“Because for your first language, it took you years and years of getting it wrong with constant reinforcement from native speakers surrounding you 24/7.”
Exactly, and that’s one reason why the idea that you can learn a foreign language by ‘speaking like a child’ does not work. Even if you are living in the country where that language is spoken.
And yes, having a good grounding in grammar for Russian or any Slavic language will definitely help you read more complicated sentences.
And pushing the logic further, although this can’t be proven, we can imagine that for millenia, humans have learnt languages in 2 ways: 1) as babies in an immersive environment with constant nurturing, and 2) as grown ups, spending time listening to native speakers and talking with them, learning about their culture, without the aid of any written material.
Most people learn to speak by listening to those around them. If the way people around them speak is considered acceptable grammar, then they speak grammatically. I am in South Carolina and educated people here regularly say “They is”, 'He don’t" “He ain’t”, and I don’t think this is the result of any training by parent or teachers. it is just how people speak. People learn from others around them, from exposure. This is also, the easiest way to learn a foreign language, in my view, lots of exposure. Reference to grammar books and being corrected from time to time can helps us notice things, but mostly we need lots of exposure, in my view.
I did not invest much time in a “grounding” in Russian grammar. I tried, but in many cases could not understand the rules, nor remember them, and their exceptions. However, after lots of exposure, I am able to go back to the grammar rules again and again, and eventually certain things stick. It is not a matter of knowing that there are cases in Russian, nor even the general rules about the reasons for the cases. That part is easy. Remembering the cases, remembering which prepositions take which cases, remembering which verbs and which other constructions take which cases, all of that requires a lot , and I mean a lot of exposure.
I certainly agree a lot of exposure is needed at the beginning otherwise there is nothing to base these rules upon. If someone gave you a list of case endings and where they’re used, before you even started, then unless you’re a savant, you won’t remember them and will be discouraged by learning. I like gradually mixing grammar into my target language. The quickest way I’ve found of remembering rules is to write a general rule and learn the exceptions through reading/ listening.