Hardly. "Keys to the kingdom" seems to imply that access to the key opens up a large number of other doors. That's the case for email (via password recovery) and password manager (via its function), but not for much else. E.g. while access to online banking is a catastrophe in its own right, it doesn't unlock many other accounts.
No, the point is, people without a password manager tend to use the same password for every account. So you steal the bank password, and it opens your email, facebook, and everything else. Hundreds of failure points. With a password manager, there is just one.
Human nature being what it is, a large fraction of password-manager users probably also reuse passwords, or nearly reuse them, which is nearly as bad. With the password manager being there for cases where some BOFH admin required two relatively-prime numbers, plus three non-adjacent capital letters, plus at least one special character that's not a star, plus a final character that's not a lower case letter, plus uniqueness with respect to your previous 100 passwords, plus a length of at least 12 characters, plus a change every 14 days.
