If you choose a strong master key this should still be secure even if a site leaks a generated sub-key/password. All you need to do is change the sub-key for that site. Both this and password managers though still can be hosed if the machine your using is compromised. Otherwise it should be secure as your master key.

Leaked passwords can be changed for this they have what looks like a version input. If the master key can be reversed from a cryptographic hash function either the hash function has been broken or you chose a really bad master key.

Although storing PINs and all the other random things some sites may use is a valid point. I am not sure I would call this less secure than a traditional password manager though.