I think one of the main healthy ingredient lost to processing is fiber. It is good for moving food through your digestive system, plus it moderates harmful glucose spikes which is very unhealthy.
Potatoes have a lot of fiber in the skin, but fries remove all that.
(I've also been told, eating potatoes are like eating a plate of sugar)
Maybe not powdered potatoes in a box processed, but the peeled boiled potatoes might not be too different to your body.
It's even been shown that just freezing and thawing vegetables can significantly break down the fiber and vitamins so your body doesn't get the benefits.
Potatoes have a lot of fiber in the skin, but fries remove all that.
(I've also been told, eating potatoes are like eating a plate of sugar)