It’s really stupid when people treat language learning as a competition. Who cares what others know? Really. Just enjoy learning at your own pace.
What is not stupid is that Lingq provides several different optional methods for self-motivation. Motivation is the most oft-noted requisite for language learning. If some folks find motivation in these competitions, then good for them. Same with that avatar thing which I find silly but from which others might benefit. I don’t do challenges and glance at the avatar once in a blue moon, but their availability for motivation of others doesn’t bother me. What I did find somewhat motivational was back when one’s known word count was displayed with each post in these forums. I’d push forward to the next round number of hundreds or thousands just because it looked cool to my petty mind. You might think that a silly motivation, but the resulting gains were serious.
Good point. I’m sorry if I gave the impression that the challenges are stupid. I should have made my point with more clarity. More power to you if you like the challenges!
So this person has 5700 known words in a week in German and they just started. There are a few possibilities here. 1) They are cheating 2) They are a native German speaker 3) They knew a lot of German before or were fluent even 4) They are highly talented and know similar languages already.
Now I can´t say which one it is, but all are possible. When I started with Dutch, I was already fluent in German, English, Danish, Swedish and Icelandic and fluently literate in French. I did about a thousand known words a day for about 3 weeks straight, working maybe somewhere between 4-9 hrs a day. That´s about 21K words in 21 days, so it is possible. I am now doing Norwegian and it´s going even faster with less work, cause there are almost no words in it I don´t understand already, cause the are the same or similar to Swedish or Danish words etc.
Cheating is despicable. There is hardly a point in doing a “challenge” in your own native language either. Doing a challenge in a language very similar to others you know, well there´s a lot of grey area there.
“What is a valid option is reading more.”
In an ideal world, yes 
I would say someone who knows a foreign language before improving on it here would (as the system suggests) first mark all the known words as known that they enccounter while reading. This is the perfect moment to reach the goals specified for the higher level challenges, isn’t it, so why shouldn’t they participate? I try to look at my own stats only and to ignore what others are doing.
What I would like to see is some form of an easier challenge you can do while being intermediate, like just reading n words in 30 days or whatever instead of having just the coin and hardcore challenge apart from the non-specific monthly lingQing challenge.
I remember someone (and I think it was someone from LingQ) commenting that although many people who were already super motivated language learners probably didn´t need the avatar at all, it would probably be good for a lot of other learners so they could motivate themselves. This came as a response to negative comments on the avatar, telling LingQ to prioritise functional features instead.
The funny thing is I´m a polyglot and have used LingQ manically at times and generally spent great amounts of time learning languages without much of any outside motivation and I still enjoy having the avatars. It´s just one more little thing to motivate me (ok so I´ve finished Advanced 2, but I don´t have all the background items etc.) and I have children I can show the avatars to, who enjoy helping me choose clothes and items for them.
So again, different things to motivate all sorts of different people.