Ah I see, apologies, I understand your concern.
If we define 'big' and 'small' as being above or below the average (mean) value, then you're quite right that it breaks down for many cases, like the one you gave. But if we define 'big' and 'small' relative to the middle (median) value of the distribution, then it becomes a robust result. Hope that helps!
For anything more than 10^6 km away and less than 10 metres in size, we just wouldn't see it. We have only just noticed some enormous lumps on Ceres, and it seems a whole planet has evaded detection until now.
I don't think it's particularly likely we will find a vN probe. But to consider their non-detection to be of statistical significance is, I think, an overestimation of our technological capabilities.
If we are talking about alien life in general, I completely agree. But this calculation relates specifically to intelligent life. And from that collection we can deduce something, as explained in the website. The calculation assumes nothing about the presence of water or carbon.
Indeed, in fact in most situations it's impossible to be both an ordinary individual and be in an ordinary group.
Hypothetically, let's imagine there were 10 normal-sized planets with 10 people each, and 1 big planet with 1 million. In this scenario everyone is either on a strange (big) planet, or they are on a normal planet but they are not typical individuals, because over 99% live on the big planet.
"I am more likely to have been born in a high population country than a low population country"
And you don't think that's useful?