It pretty much became the Seven of Nine show when she arrived.
Actually it didn't. I researched this for an article in Star Trek Magazine
about the fourth season and Seven's arrival. I determined that in seasons 4-7, Janeway remained the character who was the (or at least a) focal point of the largest number of episodes, with Seven in second place. Seven's prominence roughly equalled Janeway's in season four, naturally enough since she was a new character whose personality, backstory, and relationships needed to be established, but in later seasons she was generally second in prominence to Janeway -- except in season 7 where the Doctor came second in the number of focus episodes and Seven was third.