I'm not "learning by immersion" in a sense that I'd just flood myself with stuff.
I do it methodically and systematically.
I found that the least intrusive way to do that was by chatting a lot with Japanese friends on first Twitter, then smart.fm (where I simultaneously drilled vocab with an SRS) and Lang-8 (where I at that time wrote a lot of texts to be corrected by native speakers), now on Facebook (where I observe and mimic).
I'm still doing that, despite living "in the middle of the action" now, because it provides me with both production and with reading practice, which does a lot for me nowadays.
Because of the nature of chatting, which is interactive and requires you to understand and react properly, you learn pretty fast. You'll recognize certain patterns, you'll be able to discriminate with whom you're chatting by looking at the text, to a point where you wouldn't even need the name of the person.
One of the guys I'm acquainted with uses a lot of ~つつある、相当, another one uses a lot of 余計 and certain casual patterns such as みな. I picked up expressions like ピンとくる, because it reverberated somehow and I only had to see it once.
While this sure is immersion in a sense, it's also "study", because I actively try to make sense of every little detail, or I'd mistake things being said to me and couldn't keep the conversation going properly. I asked for clarification a lot of time in the past, and had people explain to me things grammar books didn't tell me.
Yea, I also did oldschool grammar studies. I sat down with Michel Thomas, Japanesepod, Tae Kim, IMABI, several books and other websites. Sometimes to try to find out how to express something specifically, sometimes to learn something randomly. And reading grammar books from cover to cover is just fun sometimes.
I eventually grew out of those shoes and now just use the language and get more by osmosis.
Only when I'm interested in a new topic, I'll search for a list of terms on the net, and sometimes in German or English, when the Japanese isn't available, and then translate them into Japanese (with the aid of natives) and drill those lists on Quizlet.
I don't do that to make it active vocab, so I don't give a ***** about how certain things are being used, or when, and when not. Making flashcards for me has to be as quick as possible, too, as to not waste time with the creation process and technical details, because I don't wanna get good at making cards, I wanna get good at understanding new words.
Deeper nuances don't worry me so much. I just learn them with an initial hook and then let my encountering these words in my chosen subject texts teach them to me in more detailed ways.
SRS really is a chore.
It doesn't matter for me if there's a need to learn, I never worried about that, to actively prevent burnout from happening - and Kanji studies brought me pretty close to that. Even now, with RTK, I sometimes just stop and read stuff for a while, maintaining my decks with reviews of past stuff, without adding anything new. The other day I watched a series on how to write beautifully on Youtube, which taught me the concepts of とめ、はね、はらい, because I found my characters to be extremely ugly and Japanese people told me "yea, they look good, but they don't look like a Japanese person had written them", which bothered me more than learning more Kanji at that time.
The result is that I learned 1400 Kanji in 2 months, then 200 more in the next 1 - my acquisition rate went actually down by 500 words a month.
I sometimes wonder if I should just drill the rest of those Kanji in one go, only to get done with it, and then really learn them in-depth via other methods.
SRS has failed me, because how effective something is for you depends on a lot of factors, and one of them is expectation. I expect a long, boring review session with frustrating fails and that's exactly what I get.