The only character who had received a genuine promotion was Tuvok, which is odd considering that he had started the series as a lieutenant-commander but was demoted by the writers to First Lieutenant without any explanation. Paris got demoted from lieutenant j.g. to ensign and it took him over a year-and-a-half to regain his old rank. Otherwise, no one else got promoted during "Voyager".
And this doesn't excuse why Sisko wasn't a captain from the beginning of "Deep Space Nine". Come to think of it, his pattern of promotion followed (or almost followed) that of Michael Burnham of "Discovery". Like Sisko, she began as a commander, lost her rank completely before regaining it by the end of the show's Season 1. Like Sisko, she was finally promoted to captain by the end of her series' third season. And like Sisko, she was portrayed by an African-American actor/actress. They are the only two leading characters in a Trek live-action production that experienced this.