That approach might be at odds with the market, but I don't think it's at odds with learning. I strongly dislike duolingo - it's gamification kept me pre-occupied for a while without noticing that I wasn't making any progress learning the language. When I figured that out, I felt cheated by the app!

A long time ago I used a beta app that was being built by a high school teacher that I really enjoyed. It basically had a bunch on YouTube videos with a few different type of exercises. Unfortunately I had a busy schedule and couldn't keep up and I don't think the app was successful.

My day job is development in the education space. If you care about building a learning app, read up on learning theory / pedagogy. A concept I really like wrt language learning is "comprehensible input". Other things to consider with languages is that hearing native speakers is extremely important.

ps. wrt to gamification - I wish that people took the parts of games that I do like when they gamify an experience - open worlds, exploration, story telling, low stakes, save points, fun!