I really have mixed feeling about the advice here:
"Starting with the 5K is really setting your standards low" really strikes me as a debatable statement.
I did not start with a 5K, so it’s not even about my own personal experience. After reading the article, I think I understand your point, but given that the overall article seems aimed at newcomers to running, I don't understand why a 5K needs to be described that way. It feels very "gatekeep-y" in a way that I don't think was intended.
I'm not even questioning your experience, running a half worked for you, great. You don't like 5K, even better, we all like different things. But I know people who used a 5k as a step towards different distances, so they can figure out what they liked, and this article would pretty much have told that they were wrong. That does resonate with me.
Finally, I'll add that even without going into details like aerobic effort, anaerobic, etc ... which I'm frankly not qualified to talk about, describing a 5K as a sprint strikes me as really wrong.
I don't think there is a formal definition, but I believe that a sprint is essentially defined as an all out effort, essentially nothing past 400m. And if that's the case, a 5K is really far from that, it requires a ton of effort regarding pacing that in my mind is way closer to a marathon than it is to a 400m. Sure, it's way faster, because you're running 8 times less, but still.
Anyway, I don't want to come off as antagonistic, but, as someone who enjoys running and want to share it with as many people as possible, I really wanted to share my thoughts.