(Consider that the mental aspect of a race is inversely correlated to the distance of a race, and that muscle glycogen is generally depleted around 2 hours into a race-pace bout)
I disagree with your quoted statement. I'd say the mental aspect is equally important in the 1/2 marathon as it is in the 5k. In the 1/2s I ran, the mental part was mostly fighting fatigue, whereas in the 5k, it was mostly fighting through pain (and fatigue too, but anaerobic fatigue instead of aerobic)
However, for certain people who might be described as having "no business" at a race, the longer races are going to lean more heavily on a will to complete the distance than an ability to maximize performance. I would guess that for some people (certainly me when I was starting out) their 400m pace may not be that far off from their marathon pace.
I don't understand this mentality of running longer and longer distances. Most people should not do that; even with proper technique you're repeating over and over the same motion, same impact on the same areas. In most cases, injury is just a matter of time. Stress injuries are extremely frequent [1] and all this is part of this mentality that with suffering I'll accomplish more. And, longer distances usually equate to more injuries [1].
Strength [2] and fast twitch fibers are the first ones to be lost while aging, so it is way more effective to train those and run shorter, more explosive distances. And even more effective learning proper running technique.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2465455/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3940510/
[3] https://www.ncbi.nlm.nih.gov/m/pubmed/15462613/
Edit: added [1]
I do not agree with "no business being there", but I think the idea that being overweight/moving incorrectly and trying to run long distances will increase your overall injury risk. It should not be a surprise when a 230 lb person suffers knee and ankle injuries as a result of LDR, regardless of shoe tech.