> calling something a "null hypothesis" is just an arbitrary label that doesn't affect reality

It does affect your conclusions though.

The choice of null hypothesis in "The DK Effect is Autocorrelation" determined how the random data was generated. The hypothesis is: "nobody has any clue whatsoever how competent they are". The random data was specifically crafted for that hypothesis.

The choice of null hypothesis in this article is: "everyone roughly knows how competent they are". This random data, too, is specifically crafted for the null hypothesis.

So what does this mean? If you pick the a particular null hypothesis then you can try to argue that the DK is a statistical artefact. But it's not, it is an artefact of choosing a particular null hypothesis.

There are valid criticisms of the DK study, though. See this comment for example: https://news.ycombinator.com/item?id=31119196