Respectfully, I completely and whole-heartedly disagree with this. Life is about the journey, not about the destination. This assertion would disregard the fact you benefit far more from the knowledge gained in levels 1-30 than 30-40 or 40-60. There’s still a plethora of useful kanji in those levels, however kanji learning is subject to the law of deminishing returns. As you learn the majority of the most frequently used vocabulary and kanji, the need to continue learning less common words is reduced.
By learning the kanji up to level 35, you’ll know 95% of the kanji in the JLPT N3. As reading native material becomes easier and the kanji in higher levels can be more obscure/less commonly used, it can be the case that just by reaching N3 proficiency you may be able to read whatever native text you wanted to read. Sure, you won’t know every kanji, but there comes a point where you’ve progressed far enough that you don’t need to progress anymore: if you’ve obtained a skill level and knowledge base that enables you do what you set out to. WK doesn’t even teach all 2136 of the official Joyo kanji, so that’s something worth keeping in mind.
Ultimately, it depends on what your goals are for learning Japanese. If your aim is to be completely fluent, even being level 60 in WK is not enough, as WK doesn’t teach grammar, doesn’t help you practice speaking, nor does it help you practice listening. If your goal is to simply read some manga, or perhaps light novels, you may find that progressing to levels 30-40 is sufficient to allow you to do so. Finally, it’s important not to impose your own goals onto others, and to avoid judging their progress according to your goals.
I can see that you’ve said you were joking, so I just wanted to clarify that I didn’t write this with any ill feelings. I just wanted to set the record straight and offer my own thoughts on the prompting. I’m sure there are people out there who truly do believe that learning a language is all or nothing.
As a final note, If may offer you a piece of advice that will hopefully be of some use to you in your future on WK, remember that while all jokes may be jokes, not all jokes are in good taste. To add to what @jprspereira said, for a lot of people here on WK, their progress in learning Japanese is a deeply personal, emotional and significant entity in their life, so it’s natural that some people may be sensitive towards such jokes.