This feels unnecessary. Everyone gets it: you can't actually redesign a website with a few random mock-ups and visual updates. That so often is not the point of an unsolicited redesign.

Most of these people are young designers looking to practice, have fun or create something tangible to demonstrate some of their skills. Its clear that changing a button or making a visual change doesn't equate to UX expertise. However, for a lot of designers this material gets them attention and gives potential employers common context to evaluate them and maybe they are a UI designer who wants to display their visual skills. There are a lot of reasons to take it too seriously but I encourage young designers to do it. A redesign can help me evaluate certain skills in a junior candidate and they are fun to look at. Redesigning stuff is fun, who cares if you want enjoy yourself.

So, I'm not sure who this for. Convincing a designer not to do a redesign of a website and post it on their blog? What's the harm? These redesigns don't actually change the industry understanding or perception enough to matter. We need to calm down and just enjoy these redesigns for what they are.