The point is that all these 'claims' are purely subjective.
For example, swapping from Clarins to Nivea doesn't 'prove' that Clarins works any better than maybe Simple or Boots No 7. It just 'proves' that there was something in Nivea that caused some spots to appear. It's usually the perfume or preservatives in products that cause irritation.
Just because one product doesn't cause irritation, doesn't mean it's worth the cost or will stop your skin wrinkling or sagging. It just means it's not irritating your skin and providing a level of moisturisation that works for you .
I first used Clarins 40 years ago when it was a really niche product. It was far less fancy than it is now, and in my opinion a lot better. Now it's full of perfume and goodness knows what - all hype.
You're paying for the lovely jars and bottles, the acres of paper that come in the package telling you in pseudo-science what it's supposed to do, the glossy counters in stores, the advertising in glossy mags, the sales assts.
I think a true test of a high end over budget ranges would be to try 3 or 4 of each and then compare. My guess is that one budget range item would work just as well.
Good skin happens from the inside out. You can't expect anything you put on the epidermis to make a real difference other than provide a slightly smoother surface while you use the product. Collagen and bone structure as well as fat are the the basis of good skin and they come from lifestyle genes and lack of damaging UV light!