I still repeat my seed phrases in my head every morning when i wake up, it's a fun little ritual I have. And havent had to look at that single card for a loooong time. Eventually I burned it too.
Anyway, that's how I did it.
Ahh I know this memorization method and that was taught when I was in elementary school, and it was indeed effective. I must admit that I wrote down some phrases and read them every time before and after waking up, when I was going to take a shower, I was even taught to memorize vocabulary in various Arabic and English languages at that time. And OP's method is not much different, why is it effective? of course the process of repetition that is done routinely will increase good memory. Still backing up offline is important, but when talking about the memorization method that OP said, it is also my experience.