Again, no that's not how it works. Today in the browser (at least the one named similarly to you :-) the password manager stores and pre-fills the passwords. So if I want to go to my account balance page, I go to the login page (via normal bookmark), and it fills in the password for me, and I click login. Then I get to navigation, where I can go to the page I want to see.

In some casea I can get halfway there because the site is smart, and if you bookmark a page, it takes you to login, and and after you login automatically takes you to the page you were trying to get to.

A deep bookmark would just automate that process, it would not reduce security. In either case, it's as secure as your password manager.