Why do you suppose he is the best judge of that? Surely that’s not the case for other professions that offer products or services, like medicine, airplane piloting, etc.
Again, please do not compare oranges and apples. This is not about the uncle in question creating a professional product for others, it is about him arranging UI elements in the way he deems fit. A better (although still imperfect) comparison is you cooking your own lunch.
This would be a terrible idea.
People complain (in the comments on this very page) that Apple’s professional designers do a terrible job. You think my uncle is going to do better?