[EmployedRussian]

Here you are using fixed passphrase and site name as the password, resulting in monosubstitution cypher, which is where the insecurity comes from.

If you use site name as the passphrase and fixed password ("password" below) instead, you end up with:

  yahoo.com:   dXgvRMjjHQvRQFvSa
  patreon.com: UdKiiXVxrCRjYe
  therapy.com: KFXUMnMnSrJLIjaB

That seems quite a bit better (though you do lose ability to print the chart for off-line use). If an attacker knows your 3 plain text passwords and suspects that you use passwordchart.com, you are still in trouble.