Atlo: Mind asking how exactly do you learn Japanese? When it comes to tools that are not best fitted for the job I always say - ''
As long as it gets the job done.'' The problem with this approach is - that sometimes means trying to hammer a nail with a screwdriver.
I.E.: There is also such a thing as a completely wrong tool for the job It would be really hard to gauge what the advantages and disadvantages of Duolingo are compared to your Japanese approach - mind you - if it can even be applied.
Basically: There are some resources online that will tell you the same thing (if you're self studying). Get an app called Anki, for flashcards. I won't say the flashcard method is the most perfect one, but it worked for me. We'll get to the flashcard deck you'll use later. Now combine it with
Tae Kim's grammar guide. The best part about it is that it just works. It doesn't go in circles trying to explain a concept, it just figures a way to get the idea across. A bit basic, doesn't have some of the flair other guides have, but I always came back to it and it's the only guide I finished. It's brief but it has enough punch to get you to understand like, 95% of all grammar you'll ever meet. There's only like two or three points that I had to look up elsewhere and it's not often that I find them.
Now the Anki deck is Core 2k/6k. This deck has the words in their kanji form on the front, on the back you'll find the reading of that word, a voice example of the word itself spoken by native speakers, a SENTENCE, and ANOTHER voice example of the sentence. And if you want, pictures for the first 2,000 flashcards. See, this is where other languages fall short. They don't have something like the Japanese Core decks. It's either just word definitions or text to speech voice examples that won't necessarily get my ears used to how native speakers of German and French say their stuff.
And as for Duolingo, well...it's more gamified than my tastes would like. Most of the time I'm just "learning" the basics of Japanese over there, because I'd rather get XP and keep up that streak over putting a tiny bit of effort to the languages I'm lacking in, and I happen to be way better at basic, kiddy-like Japanese than the other two. Duolingo is also a bit slow, but with Anki you inherently learn new words and expressions every day and still review old ones, and passively too That and Duolingo punishes you for making mistakes
unless you pay of course, and it turns out all these Japanese resources and tools are free (unless you're on iOS, then Anki costs money).