I actually love the deterministic idea, but in practice it does have one big downside compared to a password manager which is comprehensiveness (ie the ability to store all information for all accounts).
* Not all sites use email, and I can’t always remember my username (it’s different on different sites because of what names are already taken), so I will store username and password together within the password manager. HackerNews is a good example of this.
* You can store accounts that are shared, where you generally don’t get to choose the password. For me this includes my parents billing account for their ISP.
* Some corporate accounts block historically used passwords and require changes to the password every X days. This is not compatible without further salting the word.
* Some things have different password requirements - e.g. each bank account requires a different 6 digit pin and several layers of challenge/response questions that I will have also answered with random digits. Why banks choose to protect my account based on my mothers maiden name I don’t know, but as far as they are concerned her name iNv84%N:1. Also I can’t always change the pin - one investment account I use insists that it’s randomly generated and posted to me via snail mail! Others will choose your online banking username for you and I need to store that too - I’m looking at you HSBC with your usernames like IB9173628!)
* You can store other documents in a password manager. I have my credit card details in so I always have them anywhere I go, and my password details.
1password can handle all the above weirdness. Now granted, if someone were to get hold of my password manager... that’s a game-over situation and a really bad time. But my personal requirement is storing 100% of the information I need on all accounts rather than some of the information required on most of the sites.
Although I really like the deterministic approach, it comes with its own design compromises because there is no perfect solution in this space.