I found this comment interesting (because it explained why the content was completely unreadable) and useful (because the sub comments lead me to a solution that allowed me to read this content).
I can't tell if that is the case here, but a lot of time it is the original author posting their content on HN because they want feedback from smart people, so hopefully this is useful to them as well and they unbreak their website.
Please consider revising this rule. It seems like such complains should be allowed when the website is completely unusable.
Btw, this applies at the meta level too: having this rule generates objections to the rule, such as what you posted here or this example from the other day: https://news.ycombinator.com/item?id=36904267. But not having the rule generates more objections, along the lines of "why do people always post these offtopic complaints about page formats etc.? they're so boring..."
Formatting complaints wouldn't be so bad if they would hang out somewhere down the middle or bottom of a thread - but for some reason they nearly always get upvoted to the top. They're reflexive reactions that are quick to appear—much quicker than the thoughtful, reflective reactions we most want on HN, which are slower to process and write*—and then they get upvoted because of co-feeling ("me too, I was annoyed by $thing too") and then stick at the top because of inertia, choking out everything on-topic. Then they really generate complaints ("why is everybody talking about CSS padding instead of $topic? what is wrong with this place? jesus christ you people") and it just gets worse from there.
The point is that the dynamics aren't stable - you can't have discussions about this kind of thing that stay in their lane and don't crowd out the important things. That makes the value of this rule much higher than you'd guess at first sight - once the problem dies down, it doesn't seem so bad, and then the rule seems excessive.
Oh and one last thing - there's nothing intrinsically wrong with comments like https://news.ycombinator.com/item?id=36914336. As you say, it's helpful and useful information in its place. That it can't stay in its place is a systemic problem, a tragedy-of-the-commons thing where no one is doing anything wrong at an individual level and yet the end result is undesirable. Most of the tricky moderation problems are like that.
Bottom line, this rule is in the running for "best new site guideline of recent years" even though it doesn't feel like it!
* https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...