I also found that having one master password like that is probably not so clever. But who is saying that you have to use the three input fields like this? I came up with my own system. So I'm kind of using lesspass now as a password generator. The generated password I save in keepassxc along with the rest of the information. In most cases I don't need to consult the vault and can generate the password on the fly but I'm not bound to lesspass at all. So in case I should lose access to the vault I can still log into most sites.