It does make sense that Janeway would demote Tuvok after he played a key role in the "Prime Factors" mutiny. And if that really happened, then we might argue that Janeway never ever promoted
anybody during the course of the mission. She merely restored the ranks of those she had demoted, namely Tuvok and Paris. Perhaps she felt she wasn't authorized to do true field promotions without contacting Starfleet - and so never promoted Kim, either.
The original assigning of rank to the Maquis notwithstanding, of course. But she might have argued that those never were real ranks...