Your system might be secure. But, given that the vast majority of websites these days seem to require some kind of login in order to interact with them in any way, using a system like yours would drive me mad and waste so much time I'd likely end up adopting really bad practices like using memorable or repeat passwords. Just so I could speed things up a bit by being able to remember some of them, without having to decrypt and open up a text file to copy/paste login info, every time.
Which would, of course, be LESS secure than using a password manager.