This is absolutely not true, it depends heavily on usage patterns of the password manager and its features. Not all are browser extensions that autofill, and even if they did, sites change their domains for auth occasionally that break this functionality (or more often, signup is on a different domain from auth) meaning you must manually copy-paste your password somewhat often if you don't meticulously, and manually, maintain your domain list for a credential. The average person is *not* going to do that, they're going to go "huh, it broke again" and copy paste their randomly generated password.
Please, do not give security advice you are not equipped to handle.