A password manager mitigates other threats that a spreadsheet in iCloud Drive does not, such as a program just directly reading it and ruining your life. And, anyways, password managers give you auto fill which is a significant quality of life improvement.

A memorable password is not a bad password, if done right. I have a password for both my google account and Apple ID that's easy to type because when you're in device setup you can't auto fill and so random passwords are a huge pain