You can just whatever method you are comfortable with. But the thing is, we need to encrypt seed phrase before backing it up. Could be a universal method, or as you mentioned entropy or something similar like that. I am confident about my method and I will continue to use it also I am not forcing anyone to use my method. If you like it you can use it. That's all. Otherwise you have other options to choose from.

Banks of centralized. You cannot trust anything that is centralized. At least for me, I will never trust a bank for safekeeping something that is valuable to me. Have you ever realized if something happens to that bank then your safety deposit box is at risk too? Fire, water, storm, earthquake, natural disaster, anything like that could destroy the bank and those data stored into it. If you do it in multiple banks then that acceptable. But never do it in a single bank.