Sorry for the wall of texts, but I'm very passionate about this topic. Almost everyone can be quick (as in 15:30-16:00 5k) if they really tried and optimize everything and are young enough.
This is just complete nonsense. It's like saying almost anyone could be a physics professor at Northwestern if they'd just study harder. It's not true. Most people are too stupid. Those that can do it are 4-5 sigma outliers.