correct, the point of doing something like what i'm describing is to have a system for keeping / creating N unique passwords stored only in your head, in a way that provides an acceptable amount of strength, avoids disclosing all of your passwords if one is compromised, and doesn't require you to be a savant of long-random-string memorization.

there are plenty of things that this isn't an appropriate approach for, and fwiw I wouldn't tell someone it would be a good strategy for all their passwords.

it can be useful when you have a set of longer lived passwords that you need to care about guaranteeing that the entire set can't be snarfed without holding you at gunpoint.

Your strategy doesn't negate the need for a password manager for all of your non-essential web accounts.