From my personal home-cooking perspective:
I have "instant" mashed potatoes mixes. I can tell the difference between them and the real thing, but I'll continue to use them on the ocassional weeknight when pressed for time or if I'm short on real potatoes in a crunch. I have to say, I've been pretty happy with the TRIO brand that you don't even add milk or butter to reconstitute.
I expect the fake potatoes at some level of restuarants. And a few of those "family diners" do get my patronage for some of those greasy spoon meals that can be very good. Especially on my travels in rural areas, the economics of the business prohibit using all fresh.
I had a pretty good meal in West Yellowstone last year. It was far from haute cuisine, but West Yellowstone is a very small town and doesn't have the traffic or richer clientele to support all fresh ingredients. I was happy to have a restaurant that could produce a meal for me and my family of some quality. I had the chicken fried steak. I'm a sucker for those. In that case, the potatoes were real, but I'm pretty sure the "steak" was bought pre-breaded and frozen. And the stock in the gravy was certainly not made on premise.
I use some canned vegetables. Corn and beets primarily. They're economical--and of acceptable quality and nutrition in the off season. I'm not fond of canned green beans. I'll go frozen for green beans. I prefer frozen corn too, but the cost/quality ratio isn't as strong there. I hate peas in all forms. Carrots I always use fresh and usally spinach is fresh, but a few times a year, I'll use frozen in some places.
And preserved foods, while lesser than their fresh counterparts have a long and true history in ALL cuisines. We can denigrate them, but I think we ignore our past and food heritage if we do so without balance.
I use "stock in a box" when I'm doing something big. If it's really big, it becomes practical to make a real stock, but otherwise turn to "Better than Bouillion" bases for small amounts.
As a camper/hiker, I use instant rice, instant refried beans and such things too, even some sauce envelopes occasionally. No, they're not as good. Practicality does win sometimes.
From a professional perspective, which I know about only second hand, there have been discussion on this board of some commercially produced demi that is of very good quality.
And much of what we revere in cuisine has some pretty good processing involved. Alcohols of all sorts, many cheeses, condiments...
Processing a product isn't inherently evil. But much that is processed is done poorly.