Running

I wouldn't totally dismiss the idea of arch support, metatarsal compression & heel all so quickly. I mean, I realise that running is a natural function of our bodies so we are all capable of doing it unequipped given enough practice/adaptation.

But coming from my interest in industrial design & physiology/kinesiology it is easy to see that in many cases these type of supportive technologies can make things more efficient & safer on the body.

I dont know that much about running yet but a good analogy would be the use of knee supports in weightlifting. The knee is perfectly built for mobility and withstanding forces/impacts in natural planes of motion. (no twisting) Yet the use of supportive knee sleeves is a good piece of equipment to be used always/indefinitely. It keeps the joint warm (ligaments more supple) and creates a larger artificial capsule around the knee reinforcing stability through compression. Both of these make training with weights safer, and reduce unnecessary chronic overuse damage to the knee.

I don't see this as a good comparison. The human knee and associated tendons/ligaments are perfectly suited to supporting typical bodyweight, and DO NOT require supportive knee sleeves. The human knee however is not suited to supporting 3, 4 or even 5 times bodyweight. You're putting the knee under very extreme duress there. It's like saying you can break someone's elbow by applying massive forces to it therefore under normal use it should be supported.

Obsession in being totally natural would suggest that we should all run barefoot. Even ignoring support/cushioning, it is clear to see that a deep tread will grip better than our feet in mud

Really? Why do you think we've evolved toes?

and soft rubber will grip better on concrete. Giving them a clear benefit to making running more efficient, enjoyable & safer.

I can't see how running on concrete with more grip than that offered running barefoot would, in any way whatsoever, make running more efficient.

In fact it might be possible (and I know this might seem a bit far-fetched) that adding 0.7kg of weight to your feet may actually slow one down a touch!

We did not all expect to live over 80 and avoid arthritis too, during our greater evolutionary history. We expect a lot from our bodies now, often without willing to put in the many years of slow progression and adaption to do something as "simple" as running, perhaps we do need technological assistance.

We're a lot less active than we used to be, we expect a lot less from our bodies than we did. Adaption is required, you cannot just go out and run a marathon barefoot, apart from blisters you will find that your running gait changes as you become a more efficient runner. Muscles will (unfortunately) take time to adapt to these gait changes.

The problem is, we rely on technology over what nature gave us. Folks can learn to run properly or they can use orthotics (i.e. technical trainers), it's a simple choice. But bear in mind that that technical trainers will come with a long term cost, that being injury, often through fucked up knees.