Personally I have found no joy in duolingo now that they forced a completely linear path in the tracks. I abhor it so much that I am against using it. i had like a 1000 day streak and they took that away from me through a technical issue but that's not even something i really care about... the lack of options in what i choose to and want to learn next is 1000% a worse product ux choice.
In my experience, Duolingo puts you with other folks who had a similar score to you in the previous league. I at one point was learning Italian aggressively, getting multiple thousands of points a week. I then had a week of vacation where I only did one lesson a day (totaled ~100 points that week) and was demoted. The next week, everyone I was paired with had faaaar fewer points than 'usual'.
There's no particular reason to believe that the other users and scores in the league you're in represent other real-world humans, and could simply be generated algorithmically to put you at a specific point in a score distribution based on A/B testing for what works the best to keep people engaged. And if they do pull real human scores into that list, they don't necessarily need to make that list consistent between users; so if you get second place, the real human whose score is shown in fourth place could be looking at their own wholly separate list in which they were second (with a userbase as large as Duolingo, I think of these two things as largely isomorphic). As far as I know, Duolingo doesn't document or discuss the mechanics of league formation, so even if they were manipulating outcomes like this it wouldn't be outright lying.
My experience doing Duolingo regularly was that my own score would vary significantly week-over-week based on my time and effort, and I would always land somewhere in the top four-ish spots in the "league" I was in regardless. If I were really being put together with a set of humans at the beginning of the league and the scores just played out organically, I would expect to occasionally win big or get demolished, but that never happened to me.
And my guess is that being competitive towards the top of the league but not consistently winning is the best for user engagement, so they'd have every reason to fake/engineer that outcome.
“From a god’s-eye-view, we can optimize the system to “everyone agrees to stop doing this at once”, but no one within the system is able to effect the transition without great risk to themselves.”
Each individual team is incentivized to drive their metric forward.
Done together as a whole company, this leads to all metrics dropping.
[1] https://slatestarcodex.com/2014/07/30/meditations-on-moloch/
The endless gamification, nagging, and destruction of useful features would have driven me from the site. But because I'm a technically inclined, instead they drove me to sideload an "outdated" version of the app. Amusingly it still uses the same API, so you get all the core features and then some (turns out premium or not is a client side check lol) without any of the increasingly intolerable junk of the new app.
But what I have also noted is that the activity of users seems to have fallen off a cliff, which I'd tend to assume is because the number of users has fallen off a cliff. I went from a high activity user to a near zero activity user (Memrize is a much better primary tool for learning languages now IMO) yet my place in the leagues remains nearly unchanged. So either everybody also really started "engaging" with the site much less, or they simply left.
If anything Duolingo seems to be a warning about the dangers of pursuing the maximization of metrics at any cost. Work on making a better product and utilize metrics to see how you're doing. Work on mindlessly maximizing those metrics instead and you risk not only destroying your product, but also destroying your ability to measure the damage you're causing.