[twright0]

I think it's more than this - it feels pretty unclear that the "league" feature is real in any sense.

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.