I think it's a legit concern and it worries me too.
We can only go by the articles that users submit, and then only the subset we see, which is a function of (a) randomness and (b) users bringing specific cases to our attention. If there's a bias in the stories that have made HN's front page, that bias is present in the underlying data (I mean this stream of articles) to begin with. Why might that be? Well, there are a lot of possible reasons and people would most likely dispute about those as much as they do about the underlying topic.
For what it's worth (which may not be much), all I can tell you is that we want deeply, and are trying hard, to be even-handed. At the same time, we're not going to apply some sort of mechanical both-sides balancing because, although it might make things superficially easier in the short term, I don't think it would be in the spirit of the site, and we don't do that about anything else.
The even-handedness I'm talking about is probably easier to notice in our moderation of comments, so far, than of the articles. I feel pretty confident that we've done a good job of that [1], more than I am about the articles. Perhaps that's because there have been thousands of comments, but only a handful of frontpage articles, on the topic. One consistent lesson of HN is that you can't draw general conclusions from a handful of datapoints. It takes a lot more than that before reliable patterns show up.
What matters to me is that there be principles underlying the moderation and that these get applied equally. This isn't fully achievable because there's always interpretation involved—we don't get every call right. But I think the principles are the right ones for HN (I've explained what these are in the links mentioned above), and I'm always open to hearing arguments about how to apply them more even-handedly. When people make a fair point, such as xyzelement did about the submitted URL of the OP (https://news.ycombinator.com/item?id=39621225), we're happy to change something. Another example that sticks in my mind is https://news.ycombinator.com/item?id=39146630 from a few weeks ago. That was about title, not URL, but the principle is the same.
I don't know how satisfactory this answer can possibly be but I hope it's at least clear that I hear you and care about the question.
[1] That is, when people break HN's rules in the comments, such as by posting flamebait or snark or personal attack, we flag and/or reply and/or ban irrespective of what the commenter is for or against. It might not appear that way to many readers who have strong passions on a topic, but it's not as hard to do as one might assume, especially after 10 years of practice.