This doesn’t change the fact that people often write down complex passwords. It offers a method people can use to avoid writing their passwords down, but it doesn’t say that method is widespread.

This doesn’t mean passwords are easy to guess. It doesn’t say a locked account is unlocked quickly enough to allow passwords to be at risk from repeated guessing.

This makes concrete the author’s assumption that a person’s account is more likely to be accessed without authorization if they write their password down. It confirms that the stated disadvantage of complex passwords—people tend to write them down—really is a disadvantage.

This is irrelevant. It implies users are motivated to remember their passwords, but it doesn’t say users are more likely to write down complex passwords than non-complex passwords.

This doesn’t affect the argument. The author says it’s hard to access an account by guessing a password—complex or not. This isn’t an additional disadvantage of complex passwords.