I’m glad you bring up the fact that there is a difference between input skills (reading/listening) and output skills (writing/speaking). They are very different skills and likely use different parts of the brain.
I’m going to bring up a different kind of learning that I think applies to language learning. Morse Code. I happen (after 66 years of ham radio) to be a very skilled Morse Code operator. I can receive (an input skill) at easily 40 wpm and with effort up to 55 wpm. During the telegraphy heyday, many professionals could handle those speeds and more, but the workaday telegraphers tended to stick around 20 wpm. There are reasons for this.
The way we learn Morse Code is to first memorize the pattern of dots and dashes for each letter of the alphabet. An A is dot dash (sounds like di-dah), a K is dah-di-dah and so forth. E, I, S and H are dit, didit, dididit, didididit respectively. Our pattern seeking brains pick up these repetitive patterns and use them to memorize them, but it’s a trap.
When we listen to code, we look for these patterns, almost like a lookup table, but not really. We hear didah and think A. And we do that for each letter. But that takes a LOT of processing power which takes time. It’s done by the conscious mind which is slow, lazy, easily bored, easily distracted and forgetful. So the speed at which you can receive Morse Code this way is limited to around 13 wpm. With lots of practice, some can get that to 20 wpm.
My point so far is that language learning is the same. We memorize words. We memorize word patterns (grammar), We memorize common phrases. We are depending on the slow, lazy, forgetful conscious brain to do all this. When a word comes at us, we have to consciously recall it. We have to remember what the previous word(s) were, and we have to construct a sentence of these words in our head. If we can’t recall a word, we stumble and miss the next word and quickly get lost in word soup.
At this point memorization and recall are far too slow and we are very limited just like in Morse Code, because we are relying on an inherently slow processor.
In Morse Code, the break through comes when we stop listening. In order to learn to receive/input faster, we have to stop trying to decode the patterns. With hours and hours of input, at some point, the task gets handed over to the subconscious mind with is very fast and operates in the background. We can’t conscioously pass it onto the subconsious. We have no real control over the subconscious. Soon the subconscious brain starts seeing patterns of entire words and simple phrases instead of individual letters or dits and dahs. We understand what is being sent without consciously trying to, and at higher and higher speeds. Once that ~20 wpm barrier is breached, it’s only a matter of more and more practice to double that speed to 40 wpm.
Again, I think my language study in Norwegian follows a similar path. I don’t try to memorize anything. I don’t study grammar except to “break the code” about why some word order seems strange to me.
My reading has gone from word by word to largely sight reading where I often no longer see the individual words. The conscious mind isn’t fast enough to reach that level of reading. The faster subconsious is coming into play just as it does with my Morse Code.
I’m completely “fluent” in Morse Code. I can converse with someone across the world at 40 wpm and at the same time answer questions from a visitor to my station. It used to drive my mom nuts when she would ask me to take out the trash or clean up my room while I continued my conversation via Morse with someone on another continent.
I’m not suggesting any shortcuts, nor am I suggesting any plan of study. I’m just offering a reason why just about everything seems to work. By engaging the conscious mind and overloading it, sooner or later it will pass on the tasks to the subconsious. I don’t think there is anything the conscious mind can do (flash cards, LingQ, Duolingo, etc.) to speed this up. That breakthrough will happen when it happens. We can manipulate certain aspects of learning with “shortcuts”, But overall, I question whether they are breakthroughs or just parallel paths.
Frankly, I don’t believe there have been many breakthroughs in language learning since the Rosetta Stone, and I’m suspicious of any claims to the contrary. It’s all being done with the same wetware we’ve had for a couple of hundred thousand years, and have yet to fully understand.