@drewmccormack (I work for Duolingo but not speaking for them)
I'm guessing you're talking about the gamification aspects? I get concerns about manipulation for attention, engagement, etc
But I do want to say that there *is* a lot of work that happens in the course content. Of course it's not as visible as new flashy features, but it's happening. It also depends which course you are in - some get much more love than others.
Measuring engagement is also easier than measuring learning, so... :/