Duolingo isn’t a good resource for learning a language, it’s focus is user retention
These two statements contradict each other. To learn a language you must practice it every day, week after week, month after month. It's an appropriate application of addictive game mechanics, because our motivation doesn't last long: 1-3 months for most people.
Duolingo might not be the best place to learn some languages (e.g. German), but it can be a very helpful tool for everyday practice. And stuff like streaks, leagues, and other things are rather helpful.
Not all creators are orcs, of course. But people who don't understand deliberately exaggerated comparisons might be. I believe that you understood my point. Don't start arguing over nothing.