Earlier quoted context omitted.
Yeah, the science around endurance sports (cycling, nordic skiing, rowing, running etc) has got this covered in quite the detail and does recommend that majority (80%) of your training should be aerobic - i.e. below first lactate threshold. That said, especially as you're unfit early on, doing above aerobic exercices is absolutely fine to increase toe aerobic capacity.
What I'm saying is that for the majority of people, even those who are considered "fit", don't default to aerobic system of energy when doing endurance sports because they don't have a solid enough base. They think because they're going for a 30 minute run it _must_ be aerobic, but if tested, they'd find it wasn't. To know if this is true or not would require testing and numbers and defining what's considered "fit",…
Most health focused runners should be walking at an incline or running downhill except for 1-2 high intensity interval days. There are huge benefits to low intensity activity and higher doses are almost always better. The sort of intense, grueling runs that most people do are likely counterproductive. It's like running a race every day as a workout. It's just not sustainable and unhealthy at high doses.
(Of course, if the goal is to be a runner and not simply be healthy, you'll need to push your body to a point where running is like walking but it takes a long time to do correctly.)