Cheaters make clubs less fun
There was someone in the "High XP earners" club I was in (on Android) who kept mostly redoing Hiragana 1 through 4 just to stay in first place.
They were pretty ahead in the tree, too, and they only did this when someone took the first place from them.
Today I wrote a comment "That Hiragana 4 sure is tricky, eh!", hoping they'll realize how silly this looks, but was kicked out of the club :)
Oh well. It seems some people are here to learn, and some are here just to earn meaningless Internet points. More power to them.
I agree this is ridiculous.
I want to point out though, perhaps having clubs titled things like "High XP Earners" could both attract and encourage this sort of behavior. It reminds me a little bit of how in the mainstream educational system, having awards and clubs (honor societies) tied to things like GPA encourages people to focus on grades rather than learning.
I find behaviors like you described abhorrent, personally, but I remind myself that people are a product of our society, and many societies place heavy emphasis on external measures of success and learning. I rarely find an educational system that uses grades or any quantitative feedback the way I think it would be best used -- as an indicator of progress to help students to assess their own progress, with an eye towards optimizing their own learning in the long-run.
This is how I use DuoLingo XP.
I find XP useful because it gives me a coarse indicator of my progress. I know from experience that I start getting comfortable in a basic conversation around 10,000XP, and I start being able to express basic ideas and read/understand a few isolated things, much earlier, around 2500XP. I've found this progress to be remarkably consistent for me across different languages, i.e. when a language is harder, I have to put more work into reaching a similar XP point.
The club name along sounds like it's inviting cheaters. I often re-do early lessons like the Hirigana and Intro lessons because I want to make darn sure I can run through them without getting a single incorrect response, regardless of whether Duolingo thinks I need to strengthen my skills or not. I'm just a slow learner.
Frankly, it's nice to go back and coast through one I've done before while killing time waiting on someone, sometimes… while saving the more challenging new material for times like now when I have my full concentration to give to the lessons.