Yes, We can learn from Islam where many wise people have memorized the entire Quran. So I think memorizing the key of only 12 and 24 phrases is not very strange and surprising. When we take exams in school and college, we memorize the answers to those questions after reading them a few times and when the exam is over, we write them down correctly, and if the answer is correct, we can achieve good results in the exam. So I think memorizing the seed phrase of this kind of wallet is not a difficult task, those who are more wise will read it carefully a few times and it will remain in their brain for the rest of their lives. Anyway, I have memorized one of my wallet keys which I can easily write down, and I think this memorization is the most secure. Although writing it down in a notebook may be easy, but if it is lost, someone else may be able to access it later. So in my opinion, wise people memorize these few words so that no one else can access their wallet key.
It is not about maybe you can actually memorize the phrases, there are people that can even go as far as been able to memorize twice or thrice of those words and even accordingly but the question is always about it been the best option and I think you are simply wrong in the sense that you said it is the best choice. For me I think it is not the best choice. The example of the Quran memorizers you bring they are mostly practicing this memorization every time and this is why it is still fresh in their minds more so if you look at the history of how it was written it was to preserve it and that shows the importance of writing down the words.
The memorized can have a brain damage either from an accident or another way and simply misplace those words arrangement, the memorize can also loss his live and that means the whole asset is gone. So there is nothing wrong about memorizing the seedphrase but there is nothing better than still having the words written down and stored in secure places.